INVERTED MICROSCOPE. 381 



the instrument is used, and the conveniences arising therefrom. 

 In examining an object with this microscope the object is 

 arranged in the ordinary way; when liquid it is placed in a 

 watch-glass, or such glass cells as are convenient to use. In 

 employing re-agents they can be added and their effects 

 watched immediately, for it is readily seen how the eye guides 

 the manipulations on the stage, and looks into the instrument 

 almost at one and the same time — a circumstance that facili- 

 tates ami renders highly satisfactory all such operations, as 

 nearly two years' experience has convinced- me. 



With this arrangement we need not hesitate to employ 

 hydrofluoric acid among our re-agents, as Prof. Bailey has 

 already done, for the purpose of settling, in a most ingenious 

 manner, that the markings on certain microscopic siliceous 

 animalculse are elevations, and not depressions, as they dis- 

 appear last under the action of -this acid. 



Under the supporting ring V are placed the diaphragms, 

 palarascope, achromatic condenser, etc. I have also arranged 

 a small ring of ivory, through the edge of which two wires 

 pass, that can be made the poles of a galvanic .battery, and 

 thereby subject any thing to an electric action while on the 

 microscope. The extremities of the wires may be united with 

 a spiral of small platinum wire, which would become heated 

 by the passage of the electricity, and in this state can be 

 brought immediately over the object -under examination. 



There is another and very simple method which I have 

 adopted for heating or evaporating liquids while on the stage 

 of the microscope. t It consists of a thin plate of brass, about 

 five inches long and an inch wide, with a hole in the center. 

 About an inch and a half each side of the hole there are two 

 screws projecting about the tenth of an inch. When required 

 it is placed on the stage with the projecting screws downward, 

 that prevent the plate from touching the stage, and the part 

 of the plate projecting beyond the stage is heated by a small 

 lamp. The heat is readily propagated along the plate, and 

 imparted to the glass that may be placed along it. 



In using this instrument for chemical purposes it is very 

 necessary to be able to apply the re-agents conveniently, and 

 for this purpose I place such of them as are used in two ounce 

 vials, in the neck of which there is a small drop tube, as repre- 



