GB761804A - Improvements relating to levels - Google Patents

Abstract

761,804. Levels. FILOTECNICA SALMOIRAGHI SOC. PER AZIONI. April 7, 1954 [April 8, 1953], No. 10233/54. Class 97(2) In a level which in its operating position has' part of its optical axis substantially ver- .tical and which has a sighting reticle 4 and an objective system 1-3, which forms an image of the observed field on the reticle, either the reticle 4 as shown carried by heavy plate 15 or at least one component of the objective system is positioned on said vertical optical axis and is pendularly suspended by a system of n elements each of length l = f.+ 2#(EJn/P) where # is the focal length of the objective system, E is: Young' s modulus for the suspension elements, J is the moment of inertia of the cross section of such an element, P is the weight of the suspended part, whereby small movements of the level are compensated by movement of the suspended part so that the irnageof the observed field remains fixed relatively to the reticle. Preferably there are two suspension elements or groups of elements with theirupper ends fixed at spaced positions and supporting, at their lower ends in similar positions the suspended part on opposite sides of its centre the suspended part being submerged in a transparent liquid damping bath as at 16. A fixed reference recticle 8 and an eyepiece system 9 provide a check on the positioning of the level and the free suspension of the sighting reticle 4 which is brought to the view of the eyepiece by the optical system 5-7. In a modification (Fig. 4 not shown) a part of the objective system is pendularly suspended and the pentagonal prisms 1, 7 are replaced by 45 degree prisms, the eyepieces is below the level of the line of sight and the level is arranged to be moved vertically as a whole.