METHOD OF MOUNTING OBJECTS IN FLUID. 



287 



menced this plan of mounting, thin glass was not to be met 

 with, he was therefore obliged to use a stout piece of mica ; 



Fig. 18). 



Fig. 180. 



with this his objects have kept perfect for many years. Mr. 

 Holland, whose name has been frequently mentioned as the 

 inventor of the triplet object-glass, has recommended* a cell 

 of the form represented by fig. 181, as useful for many objects 

 that require a high power. a b 

 exhibits a glass slide, on which is 

 painted, with white lead (worked up 

 with one part linseed-oil and three of 

 spirit of turpentine), a pond or cell,c c, 

 enclosing a space, d. Glasses so pre- 

 pared with cells of any size or shape 

 must be allowed to dry before they are used. The method 

 of mounting objects within this form of cell is thus described: 

 — " A drop of fluid containing the object is placed within 

 the space d, and a piece of mica of the same size as the 

 part painted dropped on the fluid; but care must be taken 

 that the drop be not in sufficient quantity to touch the inner 

 margin of the cement. That being accomplished, take some 

 almond oil in a hair pencil, and pass it lightly and slowly 

 round the edges of the mica: the oil will insinuate itself 

 under it, and will surround the object without mixTng with it. 

 When the oil is cleaned off, a coating of the white lead may be 

 laid round the edges of the mica, extending about one-tenth 

 of an inch within and without it." 



The two following methods of mounting very delicate objects, 

 such as Desmidiese, have been recommended by Mr. Thwaites.f 

 The first consists in marking out on the glass slide a cell of the 

 required shape with gold-size, thickened either with litharge, 

 red-lead, or lamp-black: these materials are to be mixed 



* Vol. xlviii., Transactions of the Society of Arts, page 123. 

 f Kalfs' DesmidiecB, page 40. 



