WITH THE MICROSCOPE. 63 



shallow <r//is formed by making a hole of the required size in a 

 piece of thin glass. This used to be effected as follows : Many 

 pieces of thin glass were glued together with marine glue, and when 

 cold a hole was drilled through them all. Lastly they were separated 

 from each other by heat, and cleaned with potash in the usual 

 manner. 



125. Simple Methods of Perforating the Thin Glass. Thin glass 

 cells may, however, be readily made by every microscopist for him- 

 self, according to either of the following plans : My friend, Dr. Frere, 

 takes a small piece of thin glass, and with the writing diamond 

 scratches a line corresponding to the piece of glass he wishes to 

 remove, next a bradawl or other sharp instrument is placed in the 

 centre of the space, the glass being laid upon a perfectly flat surface, 

 such as thick plate glass. A sharp tap upon the bradawl with a light 

 hammer causes it to perforate the glass, but the cracks made in it do 

 not extend beyond the line marked with the diamond. The fragments 

 of glass are then carefully removed piecemeal with a pair of fine for- 

 ceps, and the cell is complete. In many cases, however, the cracks 

 do pass beyond the line, and thus the chance of removing the frag- 

 ments from the centre is much diminished. 



The method which I have been in the habit of employing for 

 some years is this : I cement a square or circle of thin glass with 

 marine glue to one of the circular or quadrangular rings of glass used 

 for making deep glass cells, and alluded to in 127 ; the hole in the 

 centre being the exact size of that required to be made in the thin 

 glass, pi. XVII, fig. 99. When the marine glue is cold, a file is 

 forced through the centre of the thin glass. The cracks thus pro- 

 duced do not run across that part of the glass cemented by the 

 marine glue. The edges may then be filed square, and the thin 

 glass only requires to be warmed in order to remove it from the cell. 

 It may now be fixed upon the slide at once, or cleaned with potash 

 and kept with others until required to be made into a cell. 



In order to perforate the thin glass in making thin glass cells, 

 Mr. Brooke takes two firm brass rings, ground perfectly flat, the 

 diameter of one being a trifle less than that of the other. The piece 

 of thin glass to be perforated is firmly pressed between them, and 

 the writing diamond carried round so as to scratch each surface. The 

 circular piece is then removed by a slight tap upon the surface on 

 which the smallest circle has been scratched. 



120. Deeper Glass Cells. Supposing a cell a little deeper than 

 ;any of the above is wanted we may proceed in a different manner, 

 vpl. XVII, fig. 100 ; a piece of plate glass of the proper thickness is 

 to be cut with the diamond to correspond with the outside of the 



