WITH THE MICROSCOPE. 47 



on the grinding slab. The slides now in common use in this country 

 are three inches in length and one in breadth, and I cannot too 

 strongly recommend the observer to employ slides of this size only 

 for microscopical purposes. They should always be made of plate- 

 glass, and pieces as clear as possible should be selected. 



84. Thin Glass. An object placed for examination upon a glass 

 slide is always protected with a piece of thin glass before it is placed 

 upon the stage of the microscope. Thin glass now used for micro- 

 scopical purposes is called cylinder glass, and is manufactured by 

 Messrs. Chance, of Birmingham. It may be obtained of different 

 degrees of thickness. Thin glass in sheets should be kept in fine 

 sawdust, and it is very readily broken, in consequence of being im- 

 perfectly annealed. When cut up in small pieces, it should be kept 

 in a little box, with a little powdered starch, which prevents the pieces 

 being broken. For cutting the thin glass an instrument termed a 

 writing diamond is employed, and this is also used by some observers 

 for writing the name of the preparation upon the glass slide. As a 

 general rule, however, I think it better to write the name of the speci- 

 men upon a small label which can be gummed to the glass. 



Glass Cells are described in 124 to 135. Ordinary thin glass of 

 various degrees of thickness, and already cut into squares and circles, 

 may be obtained of Messrs. Claudet and Houghton, High Holborn. 

 For the very high powers the thinnest pieces must be selected from a 

 considerable quantity. Messrs. Powell and Lealand supply the thin 

 glass for use with their twenty-fifth. See part V. 



Tin cells are referred to in 1 1 8. 



85. Watch-Glasses of various sizes should be kept by every 

 observer, as they are convenient for many purposes. They cost about 

 a shilling per dozen, and may be obtained of the watch-makers. The 

 lunette glasses are useful for examining substances in fluids with low 

 powers, as in these we are enabled to obtain a considerable extent 

 of fluid of nearly uniform depth. 



The little porcelain moulds in which moist colours are kept, and 

 the little circular and oval shallow dishes, are most useful for soaking 

 microscopical specimens in various solutions prior to examination or 

 mounting. They may be covered by circular pieces of glass. 



86. Glass Shades. Every microscopist should be provided with 

 from six to twelve small glass shades from two to four or five inches 

 in diameter, to protect objects which are being mounted from the 

 dust. The cheap slightly green propagating glasses, now commonly 

 sold at all the glass shade shops, are most convenient for this purpose. 

 They cost from id. to $s. These shades are figured in pi. XVI, fig. 87. 



Glass slides, thin glass and watch-glasses are included in many of 



