78 HINTS TO MICROSCOPISTS. 



focus, and forms one of the best instruments that can be desired for 

 throwing light upon an object viewed as opaque. 



Mr. George Gwilt was the first to use the polished silver concave 

 reflector for viewing opaque objects in the manner in which Mr. 

 James Smith, under Mr. Gwilt's directions, fitted one to his micro- 

 scope ; it is the most simple and effective means yet devised, and the 

 expense but little. Such a mode of illumination is preferable to 

 that of the Lieberkuhn for more reasons than one. The first and 

 very essential is, the not being obliged to cut up objects into pieces, as 

 small or smaller than the stop, but the whole wing of a butterfly may 

 be mounted, and every part of it easily seen. By this mode of illumi- 

 nation, also, a greater effect of light and shade can be thrown upon the 

 object, so as to define many objects, such as the markings on the 

 scales of moths, &c. ; the disadvantage of the Lieberkuhn being, that 

 the light is thrown too perpendicularly, and this effect is in a measure 

 lost. 



Glass for mounting objects. The best glass for mounting objects upon 

 is what is termed the best flatted crown, which is sold by the super- 

 ficial square foot. Messrs. Chater and Haywood of Thames Street 

 always keep a stock, and will accommodate microscopists. 



The very thin glass is to be obtained of Mr. Drake, Jermyn Street, 

 St. James's, who has for some time turned his attention to the subject, 

 and has manufactured an article the y^th of an inch in thickness, 

 which may be obtained for three shillings and sixpence per ounce. The 

 thicker kind, ^-th of an inch, may be had much cheaper. 



Mica, or Talc (as it was formerly called) is now almost entirely super- 

 seded by the introduction of thin glass ; it is very readily scratched, 

 and is seldom obtained free from cracks. Those in the habit of mount- 

 ing objects, never recommend the use of this substance for covering 

 objects, when the thin glass can be obtained. 



Cutting Glass. Two kinds of diamonds are used by microscopists for 

 this purpose. For cutting ordinary crown, or plate-glass, the common 

 glazier's diamond is generally employed ; but for the very thin glass 

 this instrument is by no means adapted. For this purpose a good 

 writing diamond is requisite, which should be brought to a very fine 

 scratching point only. To cut the discs of thin glass for covering ob- 

 jects, strike a circle of the required dimensions on a piece of card-board, 

 and cut it out with a penknife. Place this pattern over the glass, and 

 pass the writing diamond around the edge of the circle, until it has 

 scratched it. A mere scratch is sufficient to enable the operator easily 



