The Portable Collimator. 



For use with Collimator A or B, for testing theodolites, by measuring and repeating angles in th* 

 manner these instruments are manipulated in the field. It ran be set at any angle or h.'iu'lit. 

 It is a valuable aid in adjusting instruments with fixed angles, etc.; and also serves a varit ty 

 of purposes where distant and fixed sights are a necessity in the shop. 



NOTB : The above procedure of measuring and repeating angles, by sighting at two collimator objects 

 placed at any desired angle with the instrument, might be profitably adopted in the primary instruction of 

 students at polytechnic schools before putting them on actual practice in the field. For this purpose alone the 

 collimators may be of a most primitive construction. Any two cheap spy-glasses that can be bought in a store 

 will answer, and the field of view can be simply scratched on the silvering of a mirror. The latter should be 

 placed in the principal focus of the objective of the spy-glass. There is no need of a spirit-level. The whole 

 apparatus can be improvised in any well lighted basement where it is not apt to become disturbed by sudden 

 jars and vibration of the building. Where there is a well-adjusted wye level or transit at disposal for this pur- 

 pose only one such collimator will be needed, and when they are placed opposite each other at a distance of 

 about ten feet, so that an instrument can be readily placed and operated between them, they will then afford 

 an excellent means ot making the telescope adjustments by reversing the telescope of a transit upon a point, 

 or successive points, in the opposite direction as explained on page 49- 



In treating a similar subject (also on the same page) it is assumed that the geometrical and optical axe? cf 

 the two telescopes are truly coincident with each other (a condition requiring some skill to make) in order to 

 adjust the line of collimation in a transit telescope. By employing a cheap collimator of the above kind, so that 

 the telescope can be reversed on the collimator object, this assumption becomes, however, invalidated, as the 

 adjustments can be made precisely in the same manner as in the field. To test tne adjustments for nearer dis- 

 tances it will then only be necessary to set the collimator object slide at places corresponding to these distances. 



The use of such an apparatus will give the student clearer ideas of geodetic instruments and the optical 

 principles upon which they are based, and every large engineering department ought to be in possession of 

 an improvised apparatus of this kind. Much valuable time, which must otherwise be spent in the field, can 

 then be saved. 



C. L. Berger & Sons' Auxiliary Apparatus, 



IJiied during the construction of their Instruments of Precision. 



