US2366631A - Mercury tube switch - Google Patents

Description

Jan. 2, 1945.

H. L. LAMBERT MERCURY TUBE SWITCH Filed Aug. 21, 1943 2 Sheets-Sheet 1 'IZN VE TOR ATTORNEYS Jan. 2, H, L M T 2,366,631

MERCURY TUBE SWITCH Filed Aug. 21, 1945 I 2 Sheets-Sheet 2 ATTORNEYS Patented Jan. 2, 1945 umreo STATES PATENT OFFICE :ascaazi 6 Barry L. Lambert, 1 17;2 2:1101, by

mesne assignments, York, N. Y.

to Walter J. Pickering, New

15 Claims.

This invention relates to mercury tube switches, and more particularly to those which utilize centrifugal forces for their operation. Mercury tube switches heretofore had limited usefulness owing to the time element required for each operation, or'because they were dependent upon gravity, or upon the surface tension of the mercury for part of their operation.

An object of this invention is to provide an improved mercury tube switch which will be effective at relatively high speeds, which will respond quickly to changes in speed; which will be independent of gravity and surface tension for its operation, which will handle relatively heavy currents therethrough, with which a plurality of branch circuits may be controlled in a, simple manner in a single switch, with which the speed at which it becomes effective may be varied in a simple manner, even while the device is operating, and which will be relatively simple, practicable, compact, durable and inexpensive.

Other objects and advantages of the invention will be apparent from the following description of two embodiments of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying drawings:

Fig. 1 is a side elevation of a mercury tube switch and its mounting constructed in accordance with this invention, and with a part of the protective casing broken away to show parts normally concealed and protected thereby;

Fig. 2 is a transverse sectional elevation of the same, the section being taken approximately "along the line 2-2 of Fig. 1, and having diagrammatically connected thereto a simple circuit in which the motor which rotates the switch may be selectively controlled by either of two branch circuits which are effective at difierent speeds;

Fig. 3 is a longitudinal sectional elevation through a mercury tube switch element constructed in accordance with this invention;

Fig. 4 is a sectional plan through the switch element the section being taken approximately along the line 4-4 of Fig. 3;

Fig. 5 is another plan through a portion of this switch element, the section being taken approximately along the line 55 of Fig. 3;

Fig. 6 is a longitudinal, sectional elevation through the switch element in .a plane at right angles to the sectional elevation shown in Fig. 3;

Fig. 7 is a side elevation, partly. on section, of another embodiment of the invention; and

Fig. 8 is a longitudinal, sectional elevation through the switch element of Fig. '7. V

In the embodiment of the invention illustrated in Figs. 1 to 6, the improved switch is mounted upon a shaft I which is inturn mountedfor rotation upon its longitudinal axis. The block or member 2 of insulating material is fixed upon and approximately. concentric with the shaft. The shaft-l passes through a relatively stationary support 3. which is close to, but spaced from, member 2. A spring clamp 4, which is of U- shape, is secured at the base of the U to the outer end face of the block 2 in any suitable manner. The arms of the U, intermediate of their ends, are oppositely bowed, in directions apart so as to form opposing concave seats which grip the periphery of a housing 5 and hold it in a position eccentric to the axis of rotation of the shaft I. This housing 5 is shown separately in Figs. 3 to 6, and it comprises a metal shell 6 which has a cylindrical portion which is removably secured in the clamp 4, and extending radially and outwardly from the cylindrical portion is a flattened and broadened portion 1 which may conveniently be formed by distorting and flattening one end of the cylindrical portion.

The other end of the cylindrical portion of shell 6 is closed by a plate 8 of glass which has a, coefficient of expansion approximately equal to that of the metal of the shell 6, and which is fused thereon so as to effect a tight seal for the chamber 9 of the shell 5. The flattened end portion 1 of the shell 6 is made relatively thin and flexible, so that it may flex and expand outwardly under internal pressure, and which by \its resiliency tends to return to its normal position when the internal pressure decreases. The metal of which the shell 6 is formed is one which does not combine with or form an amalgam with mercury. Relatively pure iron has this property and it is also flexible sufliciently for this purpose, and for that reason shell 6 may be made of pure iron. One may also use for this purpose any of the metal alloys which have been designed for use in contact with mercury.

The flattened portion of the chamber 9, which is the outer end zone with respect to the axis of rotation, contains a body of mercury In which preferably does not extend above the flattened portion. The remaining portion of the chamber 9 is freed of its air, and the air replaced by an inert atmosphere as usual in mercury tube switches, the glass plate 8 enabling this replacement of the air with an inert atmosphere and the subsequent sealing of the chamber 9. Extending through the plate 8 in spaced relation to each other, and to the shell 6, are a plurality of conductors H and I2, see Fig. 6. These conductors are fused or sealed into the plate 8 and extend from both faces thereof. The portions extending into the chamber 9 extend slightly into the flattened portion of the chamber so as to dip slightly into the body of mercury Ill therein. One of these-conductors, such as the conductor ll, extends slightly farther into the mercury than the other conductor l2, as shown clearly in Fig. 6.

A metal contact arm I3, Fig. 2, is secured to the outer end face of the block 2, and has 9. laterally turned arm or flange N that bears against the outer end of the conductor l2. Another metal contact arm I is also secured upon the outer end face of the block 2, extends toward the housing 5, and has an arm ll bearing upon the outer end of the conductor II. On the end face of the block 2 facing the relatively stationary member 3, I mount collecting rings l1, l8 and [9, which are concentric with each other and with the axis of rotation of the shaft l.

The base portion of clamp 4 is extended laterally as at 20, and this portion is secured by a screw 2|, Fig. l, to a metallic stud 22 embedded in the block 2 and having a portion connected to the collecting ring ll. Similarly the arm I3 is connected by the screw 23 to the collecting ring l8, and the arm i5 is connected by the screw 24 to the collecting ring 19. These screws 2|, 23 and 24 thus provide electrical connections to the collecting rings from the clamp l and the arm l3 and i5. Bearing upon the collecting rings are a plurality of brushes 25, 26 and 21, one for each ring, see Figs. 1 and 2, and external circuit wires are connected to these brushes so that through them connections may be made to the shell 6 and conductors II and I2.

The circuit wires connected to the brushes may be used to control any suitable electrical devices, such as indicating or recording instruments or ignal devices, or they may be used to control the speed of a motor M, as shown in Fig. 2. In Fig. 2, a simple circuit for controlling the speed of the motor M selectively at either of two possible maximum speeds is illustrated, but in this diagram, the connections are shown directly to the screws 2|, 23 and 24 instead of through the brushes to those parts, in order to simplify an understanding of the circuits. The screw 2|, through its collecting ring I! and brush 21, is connected by a wire 28 to a main control switch 29, and from that switch to the line wire L The line wire L is connected through the switch 29 and a wire 30 to one terminal of the motor M. The other terminal of the motor M is connected by a wire 3! to the screw 24 through the brush 26 and collecting ring 19. Included in series in this wire 3| is a switch 32. A wire 33 connects the wire 3|, between the switch 32 and the motor, through a switch 34, the brush 25 and collecting ring E8 to screw 23, and thence by arm It to conductor l2. Since the shell 8 is of metal and is secured in a spring metal clamp 4, it will be electrically connected to the line wire L through the switch 29, and serves as a common circuit connection to the mercury.

The mercury, when confined in the flattened portion 1 of the housing shell, either by gravity or by centrifugal forces created by rotation of the housing 5, will normally contact with both of the conductors II and I2 and thus electrically connect the metallic shell I with both conductors. The motor will operate and rotate the shaft l at any desired speed ratio, the shaft I being either the motor shaft and therefore rotating at a 1:1 ratio with the motor, or being driven by a speed changing mechanism so that the shaft I will be rotated at some other ratio to the speed of the motor M. Assuming that the switch 32 is open and that the switch 34 is closed, all of the current for the motor will pass through the conductor I2 and none will pass through the conductor l I.

As the speed of rotation of shaft I increased, the centrifugal forces acting on the mercury ill will tend to force the mercury outwardly with increasing pressure on the walls of the flattened portion 1. This increased internal pressure will tend to bulge the flat side walls outwardly or eX- pand them, which allows the mercury to recede at its inner surface with respect to the axis of rotation. When a predetermined speed has been reached, this recession of the mercury will have caused it to separate from the conductor I 2 which opens the circuit of the motor M. The speed of the motor then falls and as the centrifugal forces acting on the mercury also decrease, the resiliency of the wall I will tend to force the mercury back toward the conductor l2 and re-establish a circuit between the mercury and the conductor l2 and thus through the motor. The motor speed will again increase until the predetermined speed is reached, and then the circuit will again be opened in the same manner. Thus the motor cannot operate at a speed in excess of this predetermined speed, but will be held at that maximum speed within close limits.

If now the switch 32 is closed and the switch 34 opened, all of the current for the motor M will then pass through the conductor II and the mercury, and since the conductor H extends deeper into the mercury Ill, the circuit will not be opened by recession of the mercury from that conductor ll until a much higher predetermined speed is reached. The action is then the same as explained in connection with the conductor l2. The switch 34 may be left closed, if desired, or omitted, because the circuit through the wire 33 will be opened first anyway, when the mercury recedes under the action of centrifugal forces.

It is desirable to make the walls of the portion I of the shell 6 thin enough to be freely ilexible, and in such a case, this reduces the inherent resiliency of the shell tending to return the mercury to contact position with the conductors H and I2. Therefore, a pad 35 of soft resilient material, such as sponge rubber, is secured, such as by cementing, to the base 20 and under com pression against one of the flattened faces of the portion 1 of the metal shell of the housing. A pad 36 of similar material is disposed against the other flat face of the portion 1 and cemented to the face of a plate 31 which is carried on the free end of an arm 38. This arm extends across the axis of rotation of the shaft l and is secured to the block 2 in any suitable manner, such as by a screw 39.

A casing 40, which encloses and protects the block 2 and the parts carried thereby, telescopes over and is removably secured to the periphery of the relatively stationary support 3, and a screw H is threaded through a bearin 42 carried by the end wall of the casing in alignment with the axis of shaft I. This screw 4|, at its inner end, terminates in a ball-like head 43 which is concentric with the axis of the shaft and II, but it may be overcome by opposing centrifugal forces on the mercury created when the shaft is rotated. The resiliency of the pads 55 and 38 thus supplements the natural resiliency of the side walls or the flattened portion 1 of the shell 8. B turning the screw 4|, the pressure on the pads 35 and 36 may be varied, and this varies the pressure that must be overcome by the centrifugal forces acting on the mercury. This varies the predetermined speeds at which the circuits through conductors II and II will be opened.

In the embodiment of the invention shown in Figs. 7 and 8, the parts thereof which correspond to similar parts in Figs. 1 to 6 have similar reference characters applied thereto, but a different form of mercury switch element is utilized. In this form of the invention, the shell 6 is replaced by a thin metallic shell 45 that is bellows-like in character, or of the type known as rotation, which expansion is opposed by the pad 5.. When a predetermined speed of rotation is reached, the centrifugal forces acting on the mercury will be sufficient to compress the pad and force an expansion of the bellows 45 to an extent such that the mercury will recede from the electrode {2. This opens the branch circuit throughthe conductor". If the speed continues to increase toa subsequent and higher Sylphon bellows, so that it may be compressed or expanded by endwise -movement. The open end of the shell 45 is provided with an annular, cylindrical flange 41 which is received and sealed into the periphery of a cup shaped glass closure 46 having approximately the same coeilicient of thermal expansion as the metal of shell 45, with the cavity of the cup extending away from the bellows, and forming a common cavity with the interior of the bellows.

The conductors II and I2 extend through the wall of closure 46 into the mercur 48 contained in the chamber 49 to different extents as in Figs. 1 to 6 and when the bellows 45 is collapsed or expanded, the mercury 48 will move radially toward and from the axis of rotation of the memher 2 to engage with or separate from the conductors II and I2. Abutting against the bottom of the bellows shell 45 is a pad 50 of soft resilient material, such as sponge rubber, which is secured upon one arm of a bell crank lever 5|. This lever is pivoted at 52 on a bearing bracket or member 53 secured by a screw 54 to the r0- tating member 2. The other arm of the bell crank lever 5| bears against the ball end 43 of the screw 4|, so that by turning the screw 4|, the bell crank lever may b rocked in a direction to relieve the pressure of the pad 50 on the bottom of the bellows, or to release the bell crank lever for rocking movement in a direction to increase the pressure on pad 50.

A compression spring 55 is confined between an arm 56 on the bracket 53 and that arm of the bell crank lever 5| which carries the pad 50. This pring 55 exerts a pressure on the bottom of the bellows through the pad 50 and-by turning the screw 4|, the movement of the bell crank lever in a direction to apply pressure to shell 45 through the pad 50 may be variably limited.

When this device of Figs. '7 and 8 is rotated.

I the centrifugal forces acting on the mercury 48 While mercury has predetermined speed, the centrifugal forces created will be sufllcient to expand the bellows 45 againstthe pressure of pad 50 until the mercury also recedes from engagement with the con ductor II, which opens the other branch circuit through the mercury and conductor II. By turning the screw 4|, the pressure on pad 5|) and through it against the end of the bellows which is caused by sprin 55 may be varied toa considerable extent.

In both embodiments of the invention, the casing 4||'which is carried by the relatively stationary part does not rotate, and therefore, one may grasp the knurled head 44 and turn the screw 4| in either direction while the device is running. in order to vary the speeds at which the device will open the branch circuits.

When mercury is employed, the conductors H and I2 will b of a metal which is inert to the mercury, and pure iron is one example of such a metal. Alloys or other metals which are inert to mercury may, of course, be used instead.

been referred to as the preferred conducting liquid, because of its high specific gravity and good electricity conducting properties, nevertheless, it will be understood that within the broadest conception of the invention. any electricity conducting liquid may be employed, and in such a case. the metal of which the shell 8 or the bellows 45 and the electrodes H and I2 are made will be one which is inert to the liquid which is employed as the fluid conducting medium. Such other conducting liquids and metals are, therefore. to be considered as equivalents within the broadest conception of the invention.

It is believed that the operation of these devices will be understood from the foregoing description, and it will not be repeated. Because of the fact that the chamber 9 of the embodiment shown in Figs. 1 to 6 and the chamber 49 of the embodiment shown in Figs. 7 and 8 contain an inert atmosphere and are closed. any arcing that takes place will not have any materially destructive action on the mercury or conductors II and I2, and such switches can. therefore. be used, even in an explosive atmosphere, since the arc is entirely within a sealed chamber. Such a switch is not dependent upon the surface tension of the conducting liquid or upon gravity. Since the chambers 9 and 49 are sealed chambers and contain a gaseous atmosphere. any compression of the flattened portion 1 or of the bellows 45 will compress the gas within the chambers 9 or 49. and as soon as such pressure is released, the gas will tend to expand the flattened portion 1 or the bellows quickly. so that the action in making and breaking circuits can be very rapid. A switch dependent upon gravity is relatively sluggishand slow in operation, and while switches utilizing the surface tension of a conducting liquid, such as mercury, are considerably faster than gravity operated switches, nevertheless, the type above described and illustrated in the accompanying drawings is still more rapid because the compressed gas in the chambers tends to cause the mercury to move quickly with movements of flexible walls of the housing.

It will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention,

' may be made by those skilled in the art within chamber furthest from said axis being flexible to enable enlargement of said zone of said chamber ,by a greater pressure differential inside of said chamber, resilient means opposing outward flexing of said wall, a body of mercury within and only partially filling said chamber, a conductor extending into said chamber and slightly into the mercury confined in said zone by rotation of said housing, but from which said mercury may separate when its outward pressure on said wall is increased sufficiently by centrifugal forces due to said rotation to expand said wall outwardly,

and circuit connections including said conductor and said mercury which are normally connected through said mercury but disconnected by separation of the mercury from said conductor.

2. A mercury tube switch comprising, a housing having a closed chamber containing an inert atmosphere, means mounting said housing for rotation about an axis eccentric to said chamber the wall of the end zone of said chamber furthest from said axis being outwardly expansible under higher internal pressure than on the outside, resilient means abutting said wall and opposing its said outward expansion, a body of mercury within and only partially filling said chamber and confined in said zone by rotation of said housing about said axis, a conductor extending into said chamber and from outside of said zone normally slightly into said mercury confined in said zone by rotation of said housing, but from which said mercury may separate when centrifugal forces on said mercury due to rotation of said housing about said axis at a predetermined speed, expands said wall outwardly sumciently and circuit means including said mercury and conductor series therein, whereby separation of said mercury from said conductor will open a circuit through said mercury.

3. A mercury tube switch comprising a housing having a closed chamber containing an inert atmosphere, means mounting said housing for rotation about an axis eccentric to said chamber, the wall of said housing along the zone of said chamber furthest from said axis being resiliently flexible and outwardly expansible upon greater internal than external pressure thereon, a body of mercury within and only partially filling said chamber and confined in said zone by rotation of said housing about said axis, a conductor extending into said chamber and from outside of said zone normally slightly into said mercury confined in said zone by rotation of said housing, but from which said mercury may separate when centrifugal forces on said mercury due to rotation of said housing about said axis at a predetermined speed expands said wall outwardly sufiiciently, and circuit means including said mercury and conductor in series therein, whereby separation of said mercury from said conductor will open a circuit through said mercury.

4. A mercury tube switch comprising a housing having a closed chamber containing an inert atmosphere, means mounting said housing for rotation about an axis eccentric to said chamber, the wall of said housing along the zone of said chamber furthest from said axis being resiliently flexible and outwardly expansible upon greater internal than external pressure thereon, a body of mercury within and only partially filling said chamber and confined in said zone by the wall of the end zone of said chamber furthest from said axis being outwardly expansible under higher internal pressure than on the outside, resilient means 'abutting said wall and opposing its said outward expansion, a body of mercury within and only partially filling said chamber and confined in said zone by rotation of said housing about said axis, a conductor extending into said chamber and from outside of said zone normally slightly into said mercury confined in said zone by rotation of said housing, but from which said mercury may separate when'centrifugal forces on said mercury due to rotation of said housing about said axis at a predetermined speed, expands said wall outwardly sufiiciently, and circuit means including said mercury and conductor in series therein, whereby separation of said mercury from said conductor will open a circuit through said mercury, said mounting means being adjustable to shift said housing bodily toward and from said axis to vary the speed of rotation of the housing at which the centrifugal forces acting on the mercury in the rotating housing separates from said conductor.

5. A mercury tube switch comprising a housing having a closed chamber containing an inert atmosphere, means mounting said housing for rotation about an axis eccentric to said chamber, the wall of the end zone of said chamber furthest from said axis being outwardly expansible under higher internal pressure than on the outside, resilient means abutting said wall and opposing its said outward expansion, a body of mercury within and only partially filling said chamber and confined in said zone by rotation of said housing about said axis, a conductor extending into said chamber and from outside of said zone normally slightly into said mercury confined in said zone by rotation of said housing, but from which said mercury may separate when centrifugal forces on said mercury due to rotation of said housing about said axis expands said wall outwardly sufilciently, at a predetermined speed, circuit means including said mercury and conductor in series therein, whereby separation of said mercury from said conductor will open a circuit through said mercury and means for varying the pressure of said resilient means on said wall, whereby the speed of rotation of said housing which will create centrifugal forces that will force said wall outwardly enough to cause an opening of said circuit portion, may be controlled.

6. A mercury tube switch comprising a rotatable element, a spring clamp on said element, a housing secured in said clamp and having an end zone extending from said clamp in a direction radial to and away from the axis of rotation of said element, said housing having a closed chamber eccentric to said axis and containing an inert atmosphere, a body of mercury within and only partially filling said chamber and confined in said end zone by rotation of the housing with said element, the wall of said end zone being outwardly expansible upon greater internal pressure than external pressure thereon, a conductor extending into said chamber and from outside of said zone into said zone and normally slightly into said mercury when confined in said zone, but from which said mercury may separate when centrifugal forces on' said mercury due to rotation of said housing with said element at a pre- 1 determined speed are sufficient to expand said wall outwardly toallow the mercury to recede from said conductor, and circuit means including said mercury and conductor in series therein, whereby separation of said mercury from said conductor will open a circuit through said mer- 7. A mercury tube switch comprising a rotatable element, a spring clamp on said element, a housing secured in said clamp and having an end zone extending from said clamp in a direction radial to and away from the axis of rotation of said element, said housing having a closed chamber eccentric to said axis and containing an inert atmosphere, a body of mercury within and only partially filling said chamber and confined in said end zone by rotation of the housing with said element,the wall of said end zone being outwardly expansible upon greater internal pressure than external pressure thereon, a conductor extending into said chamber and from outside of said zone into said zone and normally slightly into said mercury when confined in said zone, but from which said mercury may separate when centrifugal forces on said mercury due to rotation of said housing with said element at a predetermined speed are sufiicient to expand said wall outwardly to allow the mercury to recede from said conductor circuit means including said mercury and conductor in series therein, whereby separation of said mercury from said conductor will open a. circuit through said mercury, resilient means abutting the outside of said wall and opposing said outward expansion, and means for selectively varying the pressure of said resilient means on said wall to vary the speed of said rotation at which the circuit through said mercury and conductor is opened.

8. A mercury tube switch comprising a rotatable element, a spring clamp on said element, a housing secured in said clamp and having an end zone extending from said clamp in a direction radial to and away from the axis of rotation of said element, said housing having a closed chamber eccentric to said axis and containing an inert atmosphere, a body of mercury within and only partially filling said chamber and confined in said end zone by rotation of the housing with said element, the wall of said end zone being outwardly expansible upon greater internal pressure than external pressure thereon, a conductor extending into said chamber and from outside of said zone into said zone and normally slightly into said mercury when confined in said zone, but from which said mercury may separate when centrifugal forces on said mercury due to rotation of said housing with said element at a predetermined speed are suillcient to expand said wall outwardly to allow the mercury to recede from said conductor, circuit means including said mercury and conductor in series therein, whereby separation oi. said mercury from said conductor will open a circuit through said mercury, resilient means abutting the outside of said wall and opposing said outward expansion a relatively stationary member alined with and adjustable in a direction along said axis of rotation, and means rotating with said element, bearing on said member, and also bearing on said resilient means to vary the resilient pressure on said wall opposing said expansion, whereby by adjustment of said member, the speed of rotation of said elements at which said circuit will be opened, may be changed while said element and housing are rotating.

9. A mercury tube switch comprising a housing having agclosed chamber containing an inert atmosphere, means mounting said housing for rotation about an axis eccentricrto said chamber, the wall of said housing along the zone of said chamber furthest from said axis being resiliently flexible and outwardly expansible upon greater internal than external pressure thereon, a body of mercury within and only partially filling said chamber and confined in said zone by rotation of said housing about said axis, a plurality of spaced conductors extending into said chamber outside of said zone and then, while within said chamber, extending into said zone and slightly into said mercury confined in said zone, but to different depths therein, but from both of which said mercury may separate when centrifugal forces on said mercury due to rotation of said housing about said axis expands said wall outwardly to extents proportional to said speeds, and branch circuits having said mercury in common and each a single conductor in series therein, whereby separation of said mercury from said conductors will be at diflerent speeds and said branch circuits will be opened at different speeds.

10. A mercury tube switch comprising a housing with a closed chamber and containing an inert atmosphere and a shell of-a metal inert to mercury and closed at one end by a wall of glass sealed thereto, a portion of the metal wall remote from said glass being thin enough to flex and expand outwardly without rupture when the internal pressure on said metal wall portion in said chamber is sufllciently greater than the pressure outside of said chamber, a body of mercury within and only partially filling said chamber, and a conductor extending through said glass wall into said chamber and slightly into said mercury when the mercury is confined in the zone of said chamber and against said flexible wall portion, but from which said mercury may separate when the outward pressure onsaid wall portion exceeds a predetermined pressure.

11. A mercury tube switch comprising a housing with a closed chamber containing an inert atmosphere and a shell of a metal inert to mercury and closed at one end by a wall of glass sealed thereto, a portion of the metal wall remote from said glass being thinenough to flex and expand outwardly without rupture when the internal pressure on said metal wall portion in said chamber is sufilciently greater than the pressure outside of said chamber, a body of mercury within and only partially filling said chamber, a conductor extended through said glass wall into said chamber and slightly into said mercury when the mercury is confined in the zone of said chamber .and against said flexible wall portion, but from conductor will open a circuit through said mercury. V

12. A mercury tube switch. confining, a housing with a closed chamber containing an inert atmosphere and a shell of a metal inert to mercury and closed at one end by a wall of glass sealed thereto, a portion of the metal wall remote from said glass being thin enough to flex and expand outwardly without rupture when the internal pressure on said metal wall portion in said chamber is suiilciently greater than the pressure outside of said chamber, a body of mercury within and only partially filling said chamber, and a plurality of spaced conductors extending through said glass wall into said chamber and slightly and to diflerent depths into said mercury when the mercury is confined in the zone of said chamber and against said flexible wall portion, but from which said mercury may separate in succession when the outward pressure on said wall portion exceeds diiierent predetermined pressures.

13. A mercury tube switch confining a housing with a closed chamber containing an inert atmosphere and having a shell of a metal inert to mercury and closed at one end by a wall of glass sealed thereto, a portion of the metal wall remote from said glass being thin enough to flex and expand outwardly without rupture when the internal pressure on said metal wall portion in said chamber is sufilclently greater than the pressure outside of said chamber, a body of mercury within and only partially filling said chamber, a plurality of spaced conductors extending through said glass wall into said chamber and slightly and to different depths into said mercury when the mercury is confined in the zone of said chamber and against said flexible wall portion, but from which said mercury may separate in succession when the outward pressure on said wall portion exceeds difierent predetermined pressures, and circuit means including said metal wall and mercur in common and said conductors in branch circuits.

14 A mercury tube switch comprising a housing with a closed chamber containing, an inert gas, one wall of said housing being resilient and expansible outwardly in response to higher internal than external pressures, a conductor extending into said chamber from the exterior thereof and having an exposed contact area a,sse,es1

within, and intermediate the ends or, said chamber, a body of mercury within and only partially filling said chamber, and having its exposed surface layer only shallowly engaged by said exposed area of said conductor when the mercury is confined in one end of said chamber, whereby when said mercury and said conductor are electrically connected in series to each other in a circuit and the housing is rotated about an axis eccentric to said chamber and disposed further rrom said one end than the other end, the centriiugal forces acting on said mercury will confine it in said one end and force it against said expansible wall and expand it outwardly to cause recession of said mercury from said exposed eonductor area sufilciently to open said circuit when a selected speed of rotation is reached.

15. A centriiugally operated switch comprising a housing with a closed chamber containing an inert gas, a rotatable element, means mounting said housing on said element for bodily rotation therewith and largely at one side of the axis of rotation of said element, the end portion of said housing farthest from said axis having a flexible,

outwardly expansible and inwardly movable wall,

a member rotating with said element and movable towards and away irom said wall, resilient means between said wall and member whereby movement of said member will apply resilient pressure in an inward direction on said wall, relatively stationary means engaging said member to move it in a direction to vary the resilient pressure on said wall, a conductor extending into said chamber from the exterior thereof and having an exposed contact area within, and intermediate the radially outer and inner ends of said chamber, a body of electricity conducting liquid within and only partially filling said chamber, with its exposed surface layer only shallowly engaging said exposed contact area when the liquid is confined in the radially outer end portion oi said chamber, and connections to said liquid and conductor to place them electrically in series with each other, whereby centrifugal forces acting on said liquid will urge said wall outwardly with recession or said liquid in a direction to disengage said contact area.

HARRY L. LAMBERT.

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