CELL-MAKING. 283 



table, with milled wheel below for rotation. H, brass 

 annulus or ring revolving concentrically on the table D ; 

 on the ring H are screwed two conically headed pins, J J, 

 3A of an inch apart exact, to allow the 3 x i slip to be 

 placed diagonally between them. F F, two similar pins in 



FIG. 236. 



plate D, so placed, that upon revolving the ring H they, in 

 conjunction with the pins J J, firmly grasp the opposite 

 corners of the glass slip, and cause the centre to coincide 

 with the centre of the table D. I, brass pin for more 

 easily revolving the ring H, for securing and liberating the 

 glass slip, which is done by moving the ring H in the 

 opposite direction. 



Let us now turn our attention to the practical operation 

 of cell-making. To commence with varnish cells place 

 the slide upon which the cell is to be made between the 

 pins upon Aylward's turntable, and make three rings 

 thereon (of the diameter the cell is to be when finished) 

 with a writing diamond : this operation is to roughen the 

 slip, and cause more perfect adhesion of the varnish. Now 

 take up a good brushful of varnish, and spinning the table 

 round, deliver it where the rings have been cut, in such a 

 manner that it stands up like a wall, and does not spread 

 itself more than is necessary over the slide. So soon as 

 this layer is dry and perfectly hard, another layer -may be 

 put on, and the process repeated until the cell has acquired 

 sufficient depth. The cell now requires drying or baking 



