APPENDIX. 351 



of the light, the focussing of it depends upon the lever (Z), 

 which moves the circle up and down, and with it the arm carry- 

 Ing the illuminating apparatus in tJie optical axis of the instru- 

 ment. So long ago as 1854 Mr. Grubb, of Dublin, called atten- 

 tion to the advantage of mounting the illuminating apparatus 

 on a revolving arm or arc, which he thus describes in his pro- 

 visional specification for improvements in microscopes. No. 

 1477, 5th July, 1854 : " My third improvement consists in the 

 addition of a graduated sectorial arc to "microscope concentric 

 to the plane of the object " in situ,*' on which either the afore- 

 said prism or other suitable illuminator is made to slide, thereby 

 producing every kind of illumination required for microscopic 

 examination, and also the means of registering or applying any 

 definite angle of illumination at pleasure." With but slight 

 modification, this is the plan adopted in this stand. 



The sub-stage is also fitted with complete centering and rotat- 

 ing adjustments, the latter having a graduated circle attached, 

 and fittings for carrying Darker's series of selenites, blue glass 

 disks for modifying the light, etc. In all the requirements of an 

 instrument of precision, and fully meeting the wants of the 

 most advanced modern workers, it is confidently believed that 

 this new stand has no rival. 



The price of the International Stand, Binocular, with five eye- 

 pieces, concave and plane mirrors, and right angle prism, stage 

 forceps, pliers and glass plate with ledge, is . . $325.00 



The price of the International Stand, Monocular, with three 

 eye-pieces, and the same fittings as above, is, . . $275.00 



(The Messrs. Beck manufacture several grades of objectives, 

 as will be seen by reference to their published catalogue.) 



J. W. SIDLE & CO., LANCASTER, PA., ACME MICRO- 

 SCOPES AND ACCESSORIES. 



We here quote the prices of the Acmes, and a few of the 



more important accessories. 



-3a. Acme Monocular, with brass tripod base, rotating 

 stage, iris diaphragm and substage fitting with Society 

 screw for using objectives as condensers ; in walnut 

 case with lock and handle, and drawer for accessories, $ 50.00 



