THE BOOK OF THE LANTERN. 101 



glass paper, I finish them on a square of the finest ground 

 glass, and with this beside one in making a delicate 

 drawing, a -good, fine working point may be Ue*p*t' 8 loag 

 while." ' t, 



There is sometimes a difficulty in procuring ground-glass' 

 fine enough for this purpose, and I therefore advise those 

 who feel inclined to try this method of producing lantern- 

 slides to prepare the glass themselves ; which is somewhat 

 tedious, but by no means difficult. Or should they prefer 

 it, they can purchase the glass at certain photographic 

 warehouses, where it is sold for focussing purposes in the 

 camera ; but it is rather expensive. The following direc- 

 tions will enable any one to grind the glass for himself : 



First of all, obtain a piece of glass which is both flat and 

 perfectly free from bubbles and other flaws. Be careful, 

 too, to cut it to the correct size at this stage of the proceed- 

 ings, so as to avoid all risk of mistake in this direction 

 after it has been ground. The glass is now fixed on a 

 table or board by means of four pieces of wood, nailed on 

 the board or table so as to clip its four sides. These 

 wooden pieces must not be thicker than the glass itself. 

 Now procure a piece of plate-glass measuring about three 

 inches square, to act as a grinder. Failing this, a piece of 

 ordinary sheet-glass can be employed ; but, as it will not be 

 thick enough to afford a proper hold for the fingers, it 

 should have attached to it a pneumatic india-rubber plate- 

 holder to serve as a handle. 



Now take some flour emery and mix it into a thin cream 

 with water. Put some of this on the glass, which you have 

 fixed to the table, and place the grinder above it ; rub the 



