238 



MOUNTING *OF OBJECTS. 



Fro. 64. 



holes at the required distance and then connecting them by cut- 

 ting out the intermediate space (B). These operations, however, 

 can scarcely be performed by any but regular glass-cutters, and, 

 being troublesome, are expensive ; hence the plate-glass cells 

 have been generally superseded, either by tube-cells ( 137) or by 



built-up cells. Although the 

 former may be reduced to 

 any degree of shallowness 

 A that may be desired, and are 

 made of most of the sizes and 

 forms that can be ordinarily 

 needed, yet for extra sizes or 

 B peculiar forms, shallow cells 

 may be easily built up after 

 the following very simple and 

 effective method. A piece of 

 plate glass, of a thickness that 

 - shall give the desired depth 

 to the cell, is to be cut to the 

 dimensions of its outside 

 wall ; and a strip is then to 

 \ be cut off with the diamond 

 from each of its edges, of such 

 breadth as shall leave the in- 

 terior piece equal in its dimensions to the cavity of the cell, that 

 is desired. This piece being rejected, the four strips are then to 

 be cemented upon the glass slide in their original position, so 

 that the diamond cuts shall fit together with the most exact pre- 

 cision ; and the upper surface is then to be ground flat with 

 emery upon the pewter plate, and left rough as before. This 

 plan answers admirably for constructing such large shallow cells 

 as are required for the mounting of Zoophytes and similar ob- 

 jects. 



Having had occasion, during the last few months, to mount a 

 large number of objects in shallow cells, the Author has adopted 

 the recommendation of a friend, to make use of cells which are 

 sunk by grinding out a concave in the thickness of a glass plate. 

 These, until recently, were costly ; but they are now made in 

 large quantities, and their price has been so much reduced, that 

 they can be obtained more cheaply than any other kind. For 

 objects whose shape adapts them to the form and depth of the 

 concavity, these cells will be found peculiarly advantageous ; since 

 they do not hold air-bubbles so tenaciously as do those with per- 

 pendicular walls ; and there is no cemented plate or ring to be 

 loosened from its attachment, either by a sudden jar or by the 

 lapse of time. For transparent objects, however, they are^less 

 suitable (unless manufactured with more care than is usually given 

 to them) than they are for opaque ; since the concave bottom is 

 seldom so highly polished, as to be free from scratches and rough- 



