378 INVERTED MICROSCOPE. 



The great development made in microscopic research during 

 the last twenty or thirty years is due in great part to improve- 

 ments in the construction of achromatic object-glasses; still 

 the mechanical arrangements of the instrument have contrib- 

 uted their share to facilitate observation and diminish the 

 fatigue dependent upon this character of research. In fact, 

 observers have not hesitated to make use of different descrip- 

 tions of mounting in their varied field of research, and now we 

 have instruments for general purposes, but the construction 

 of which is imperfectly adapted to certain special researches ; 

 as, for instance, the dissection of animal tissues. This last 

 circumstance has given rise to the invention of various forms 

 of dissecting microscopes, such as the Pancreatic Microscope 

 of Oberhauser, and more recently the simple and better in- 

 strument for arriving at the same end constructed by Nachet, 

 of Paris. 



These remarks are made to show how the use of the micro- 

 scope might be extended by paying proper attention to its 

 mechanical arrangements, and it is from this cause I have been 

 led to seek out a form of instrumant by means of which micro- 

 chemical research might be facilitated and enlarged. The 

 instrument about to be described is calculated to produce 

 these results. 



The great obstacles to chemical research beneath the micro- 

 scope are twofold : first, the necessity of manipulating in the 

 limited space between the object-glass and the stage ; and 

 secondly, the exposure of the most essential parts of the instru- 

 ment to the vapors emanating from the re-agents employed, 

 and the condensation of vapor on the under-surface of the 

 object-glass, thereby obscuring the view. A less important 

 obstacle is the impossibility of heating a liquid or other sub- 

 stance while beneath the microscope. 



The only way by which these difficulties can be surmounted 

 is to place the object-glass beneath the stage and the object 

 above it, with an optical arrangement of such a nature as to 

 permit observation. It was with this view that M. Chevalier 

 made a chemical support to go with his general instrument; 

 but those familiar with it know how awkward it is for manipu- 

 lation, although exceedingly ingenious, and doubtless as perfect 

 as could be for attaching to his instrument. Feeling then the 



