1895.] 



MICROSCOPICAL JOURNAL. 



157 



The Differential Object Guide. — Under this heading the 

 Zeitschrift fur wissenschaftliche Mikroskopie (vol. XI, 1894) 

 gives a description of a new stage, designed to cover a larger 

 field of usefulness than our familiar forms now possess. 



The differential object guide allows of mechanically regulated 

 movements as well as irregular ones, and achieves this by the 

 direct act of the hand, which during work does not change its 

 hold. These points precluding the use of screws, or pinions as 



interposed means of motion, the principle of " differential 

 friction " was adopted. The guide performs its functions by 

 sliding motions, and the friction inherent to these is so divided 

 among the several parts of the instrument that the greater, or 

 ruling friction is assigned to the lateral, and the minor friction 

 to the to and fro motions. If the ruling friction is allowed to 

 control the movements the effect of a mechanical stage is pro- 

 duced, if, however, the guiding hand overcomes the ruling 

 friction by ignoring it, the movements can directly be adapted 



