64 SEC. 3. MEASUREMENT. 



mm.) by means of the eyepiece-micrometer of the microscope. The micro- 

 metrical displacement of the principal slide,; which is balanced in all posi- 

 tions round the longitudinal axis of the scale column, takes place by a pecu- 

 liar contrivance, which avoids all one-sided pressure. The slide with the 

 clamp is balanced by a counter-weight suspended from the ceiling or a trestle, 

 so that its ascending and descending motion is effected with great facility. 



294. Photograph of a Cathetometer, constructed by 

 Staudinger and Co. 



C. Staudinger and Co. (F. W. von Gehren}, Giessen. 



The peculiarities of the construction may be learned from the photo- 

 graphs. The instrument has an available graduated length of one meter ; 

 the column with the counter-weight turns completely around the long ver- 

 tical axis, and is provided with adjustments, reversing telescope, and water- 

 level. 



305. Cathetometer. 



Prof. Baron von Feilitzsch, Greifswald. 



The Cathetometer consists of a central axis, and a prism turning round 

 the same. For placing the central axis in a vertical position a cylindrical 

 water-level, indicating to 10 seconds, is employed. A scale on silver one 

 meter in length, and divided throughout into millimeters, is inlaid into the 

 prism. Sliding along this is a telescope, likewise fitted with a cylindrical 

 water-level, the supporter of which is provided with a vernier indicating 



3 V mm - 



There is also a water-level, for regulating the direction of the prism. 



310. Cathetometer, so arranged as to be used for horizontal 

 measurement. Prof. Dr. Dove, Berlin. 



311. Cathetometer, by Breithaupt and Son, Cassel, with 

 riding level. Polytechnic School, Cassel (Dr. E. Gerland). 



The following improvements, contributing partly to more minute readings 

 with the apparatus, partly affording means of correction of the several parts, 

 have been added to the well-known constructions. 



The firmly placed central axis, around which the long frame and prism 

 turns, can be placed vertically by a special cylindrical water-level, indicating 

 to 10 seconds, and which is fastened to the frame independently of 

 other parts, in order that the vertical position of the axis required in very 

 fine measurements may be readily ensured ; the more so, as all othe*r 

 observations are based on the correct adjustment of this water-level. The 

 vertical position of the axis is effected in the same manner as with an 

 ordinary levelling instrument, and any deviations of the water-level are cor- 

 rected half on the adjusting screw of the same, and half by the regulating 

 screws of the tripod. 



The prism, the inlaid silver scale of which, 1 meter in length, is through- 

 out divided into millimeters, and fitted with a vernier for -J- mm., can be 

 placed in a horizontal position and parallel to the face of the scale. By means 

 of adjusting screws, and a reversible riding level, the telescope can be placed in 

 the required position. 



If this is done, the bubble of the telescope water-level will remain unchange- 

 ably in the centre during the rotation of the whole instrument on its central 

 axis, as well as during the upward and downward motion of the slider. 



