ACCESSORY INSTRUMENTS. 



123 



a swivel-joint, as seen in fig. 70, so' that it can be brought 

 near to the lamp or candle used as the illuminating body, with- 

 out moving the other parts of the stand. 



Another very convenient way of mounting the condensing 

 lens is represented by fig. 71, as adopted by Messrs. Smith 



and Beck ; the foot, a, 

 is the same as in the 

 other instrument, but 

 instead of a solid stem, 

 it is provided with a 

 short tube, b, into this 

 slides a smaller one, c, 

 having at its upper 

 extremity a cradle- 

 joint, d, connected 

 with a smaU tube, e, 

 through which slides 

 a wire arm, f, sup- 

 porting a small con- 

 denser, g. This plan 

 of mounting a con- 

 densing lens is very 

 convenient, it has aU 

 the motions of the pre- 

 ceding instruments, 

 with the great advan- 

 tage that they can 

 be effected with one 

 hand applied to the 

 arm,^ 



A smaller lens is supplied with some microscopes for the 

 purpose of further condensing the rays of the larger condenser, 

 or of rendering the converging rays of the larger one parallel, 

 whereby a greater field of view is illuminated, a plan very 

 useful where dissections are being carried on under a lens. 

 One of these instruments is represented by fig. 72. The 

 method of mounting the smaU lens is somewhat similar to that 

 last described ; it may be fixed into some part of the micro- 



Fig. 71. 



