1 86 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



tor tin's end which will imperil the absolute firmness of the sub-stage, 

 or else more will be lost than can be gained. The need of such a 

 i It -vice fur tin- most delicate and critical microscopical work is shown 

 plainly by the fact that during the past few years several ingenious 

 and practical devices have been used, nearly every principal Eng- 

 lish maker employing a method of his own. The first arrangement 

 \vas made in Powell and Lealand's sub-stage and is shown in fig. 148. 

 The nature of this device, which was suggested by Mr. Nelson, will 

 In- readily understood. It does not interfere with the general 



BAUSCH8LOMB OPTICAL CO. 



i IG. 14?A. -Attachable sta^'c with diaphragm in the plane of tlie stage. Top 

 view and cross Motion showing construct i.m of sta;;<> and utta.-lmirnt of iris dia- 

 phragm. 



mechanical arrangements of the sub-stage ; it will be seen that the 



milled ||,. ;M | A controls a MTC\\ .spindle terminating in a steel cone B. 



1 'n rotating A. I', turns, and \\itli ,-i very slow motion forces up (or 



the case may l>e) a pinC. inserted in the ba.se plate E of 



Tlie iimt imi of (' cai-ries with it Hie condenser. At 



;md foi'ming p.-irt of K : ,t the back an inner sliding 



sagainsl a spring a1 the upper end between bearings F at 



liieli are fixed upon the usual racked slide |) of the sub- 



