256 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the instrument upon its circular base, the optic axis being the centre 

 of motion. 



The leading principle followed in the construction of the stand is 



Fig. 36. 



Fig 



that when it is inclined backwards (as in Fig. 36), or turned laterally 

 (as in Figs. 37, 38, and 39), or rotated on the base-plate, a pencil of 



Fig. 38. 



Fig. 39. 



light from a fixed source will always reach the object, all the move- 

 ments, whether separate or combined, radiating from the object (or 

 the prolongation of its axes) as a centre. 



The stage rotates completely and is a modification of Mr. 

 Tolles's, in which the rectangular motions are effected by milled 



