MISCELLANEOUS HINTS TO M I CRO SCOPI S T S. 201 



ter, and of four and a half inches focus, silvered on the plane 

 slide, and backed with a plate of brass. This lens, when so 

 treated, becomes a reflector of about two and a quarter inches 

 focus, and forms one of the best instruments that can be desir- 

 ed for throwing light upon an object viewed as opaque. We 

 have used such arrangement for some time in place of the con- 

 cave mirror, and deemed it peculiar to ourselves till reading an 

 account of the above. 



APPARATUS TO PREVENT THE EVAPORATION OP LIQUIDS 

 UNDER THE MICROSCOPE. Vapors arising from the liquids 

 under observation would, by condensing on the under surface 

 of the object-glass, form there round drops, which act as so 

 many lenses, and which, arresting the rays of light in their 

 progress, would scatter them in every direction, and thus com- 

 pletely destroy the image before it could reach the object-glass. 

 This effect takes place not only when the temperature of the 

 liquid is raised by the application of heat, either directly or 

 in consequence of chemical action, but also when, in studying 

 any body by the microscope, a fuming acid is used, such as 

 the hydrochloric. This inconvenience is prevented by en- 

 closing the frame of the object-glass in a small glass tube, shut 

 at one end, whose inner surface is closely applied to the surface 

 of the object-glass. This end is then plunged into the liquid, 

 which is thus prevented from either beclouding the surface of 

 the lens or finding its way into the interior of the microscope 

 and there producing the same effect. RaspaiVs Organic 

 Chemistry. 



DROPPING TUBES, for placing on the object-holder or slide 

 any reagent whose action is to be examined, may be easily 

 made by softening a piece of glass tube in the flame of a lamp, 

 and drawing it out till it becomes capillary, after which it may 

 be broken to a convenient length. Fishing- tubes for animal- 

 may also be made in the same way. 



