ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



865 



photopbore consists of a nickelized brass tube, in whicb tbe incan- 

 descent lamp, of special form witb a straight filament, occupies tbe 



Fig. 190. 



Fig. 192. 



middle. At the back is a reflecting mirror, and at tbe front a con- 

 densing lens in an adjustable sliding tube, by which converging, 

 diverging, or parallel rays may be obtained. As the light from the 

 reflector might be objectionable in very delicate observations, a small 

 blackened disk is added ft^r covering the reflector, and a diaphragm 

 may be placed on one or other side of the lens for intercepting the 

 light from its margin. 



The battery is capable of maintaining the lamp for two hours, 

 producing a light which may bo utilized in certain cases of photo- 

 micrography, but which is much too intense for ordinary microscopic 

 research. By a slight modification of the battery, however, suggested 

 by Dr. Van Heurck, by which only 4 or 5 of the elements are coupled, 

 and the rest added as the battery becomes exhausted, or by employing 

 a lamp of less power, the exact degree of light required may bo 

 obtained. The battery evolves no fumes, and the expense of mainten- 

 ance is very sliglit, that is to say Id. per hour, including loss of zinc, 

 or less tlian a haHponny an hour if the small Stearn lamp bo used. 



Dr. Van Ilcurck concludoH as fdlows ; — "It is scon tlien that tho 



