Mi*. II. L. Smith on a new Growing Slide for the Microscope. 335 



pose the slide to be described, which appears fully to meet all 

 requisitions ; and, as it can be readily made by any tolerably 

 expert microscopist, it will, I am certain, be considered a valu- 

 able addition to microscopical apparatus. 



The whole slide, as I have constructed it, is a trifle more than 

 jjth of an inch in thickness. It consists of two rectangular glass 

 plates, 3x2 inches and about ir-,th. of an inch thick, separated 

 by thin strips of glass of the same thickness, cemented to the 

 interior opposed faces, as shown in the figure. 



This closed cell, ultimately destined to be filled with water, is 

 not of such thickness as to prevent the use of the achromatic 

 condenser — a very important requisite. The glass I use is such 

 as is employed for the small cheap looking-glasses, and is easily 

 obtained. 



The upper plate has a small hole (a) drilled through it. This 

 is effected by means of the or- 

 dinary writing-diamond and the 

 sharp edge of a broken steel brooch 

 or small rat-tail file. A hole can 

 be drilled through glass of this 

 thickness in a few minutes. Oue 

 corner of the upper glass is re- 

 moved, as at b, and a small strip 

 of glass cemented at c serves to 

 prevent the thin glass cover placed 

 over the object from sliding. Another slip of glass is cemented 

 on the lower side of the cell at d, but not extending as far as the 

 removed part at b. The object of this is to prevent the water 

 in the cell from being removed by capillary attraction, in case 

 the slide in the neighbourhood of b should be a little wetted. 

 This strip is not, however, absolutely necessary. 



To use the slide, fill the space between the two plates with 

 clean water, introduced at b by means of a pipette, and also place 

 a drop on a to remove the air. The object being put on the top 

 of the slide and wetted, is now to be covered with a large square 

 of thin glass, <?, at the same time covering the hole a. The 

 slide can now be placed upright, or in any position, as no water 

 can escape. It is, in fact, only a new application of the old 

 principle of the bird-fountain. As the water evaporates from 

 under the cover, more is supplied through the hole a, and from 

 time to time an air-bubble enters at b ; thus a constant circula- 

 tion is maintained. A cell of the size named will need replen- 

 ishing only about once in three days, and this is readily effected 

 without disturbing the object. I have been enabled to make 

 observations by means of this slide which it would have been 

 very difficult, if not impossible, to have made without it. 



