168 



CHAPTER IX. 



Description of Dr. Goring' s Operative Aplanatic* 

 Engiscope. 



It is necessary to premise that figures J, 8, 10, 11, 12, 

 14, 17, 18, 19, 20, and letter A, are drawn one-quarter of 

 the real size ; all the rest are one-sixth, exeej>t figure 23, 

 which is of the true size. 



Figure 7 represents a geometrical elevation of the in- 

 strument, just removed from its case, the body, «, being 

 screwed on, and the triangular bar, b, somewhat ele- 

 vated above the stage, which is fixed in situ. To begin 

 from the foundation, — the legs are all of the same thick- 

 ness, but tapered in breadth towards their extremities, 

 in order to obtain strength where most required. In 

 the upper one is a hole to receive the projecting pin at 

 the end of the circular bar, c. Underneath the pillar, d, 

 is a screw nut, e, which lets down, to obviate the spring- 

 ing of the legs. The pillar, d, is constructed of two 

 pieces of very stout tube, moving stiffly in each other. 

 At the head of this pillar is a socket,/^ to receive the ball 

 shewn in figure 8. This universal joint is made in the 



* Jplanatic, derived from the priv. a, and irAavT), error, means free from 

 both kinds of aberration, or devoid of all errors. 



