20-i SNYDER — A NEW METHOD OF TR.iXSITING STARS. [April 4, 



speed regulation required and the interference due to inertia a^ 

 starting. 



II. Equatorial speed that is absolutely constant but slightly 

 regulable may be given the motor, similarly placed, and the differ' 

 ing rate of motion proper to each declination determined by me- 

 chanical gearing, consisting principally of two friction disks placed 

 at right angles to each other, or by some other mechanical equiva- 

 lent. Both of these plans require special care in the constr^iction 

 and mounting of the motor, so as to obviate the communication o^ 

 injurious vibration to the transit instrument. 



III. It may in some instances be desirable to place the electric 

 motor on a separate support near the base of the instrument, and 

 then by means of a light steel shaft entering the axis of the transit 

 finally communicate the required motion to the micrometer screw. 

 All the motions and controls peculiar to either of the other plans 

 may be secured to this form of transiter, excepting that the micro- 

 meter cannot at all be driven during the time necessary for reversal 

 of the transit instrument. This limitation would in some instances 

 be rather annoying, if not destructive of facilities the method 

 should furnish. 



It is also quite feasible to place certain elements of the transiter 

 on a separate support and communicate the motion to a small slow- 

 speed alternating current-motor placed on the head of the transit 

 instrument and connected with the micrometer, and so obviate 

 practically all the mechanical and electrical difficulties. Experi- 

 ments in this direction are in progress. 



In the attempt made to actualize the electrical method of driving 

 the transit micrometer contending obstacles and facilities led, for a 

 first trial, to the selection of the second plan mentioned, namely, 

 that of gearing from a small motor of fixed speed placed near the 

 head of the instrument. In reaching this conclusion the writer was 

 greatly assisted by his friend and former student, Dr. H. G. Geis- 

 singer, who, immediately the method of the electrical transiter and 

 the conditions it imposed had been described, became enamored of 

 the delicate mechanical and electrical problem. Detail drawings of 

 a transiter of this type were prepared under the writer's direction by 

 Dr. Geissinger, and he has introduced several ingenious devices 

 which admirably meet the conditions set. The special aim of the 

 writer is to construct a form of transiter that may, without serious 

 modification, be attached to any transit instrument. It should not 

 involve a special form of micrometer nor in any way vitiate the in- 



