THE MODERN KEFLECTING TELESCOPE. 9 



becomes easy wheu the following directions are obseived. A clean, flat board, 

 having an area about twice that of the polishing tool, is prepared. One face of 

 this is covered with clean paper. Long strips of wood \ inch s<piai'e are fastened 

 upon the paper by means of fine bi'ads; these strips are placed jnst 1^ inches apart, 

 and the ends of the grooves thus foi-med (grooves IJ inches wide, ^ inch deep, 

 and of any convenient length) are closed with strips of wood. The hoard is now 

 carefully leveled. The rosin, vviien melted and softened to the proper degree, is to 

 be poured into these grooves, which serve as moulds. 



A quantity of I'osin sufficient to fill all of the grooves is melted in a clean pan. 

 Even when only a small quantity is needed it is best to melt at least ten pounds 

 of rosin, since the entire process of " tempei'ing" and pouring is more easily and sat- 

 isfactorily cari-ied on with large quantities than with small. Only lumps of clear, 

 clean rosin should be used. A gas or gasoline stove is very convenient for meltino- 

 the rosin, since the degree of heat can be easily controlled. When the rosin is 

 melted the pan is removed from the stove and a quantity of turpentine, equal in 

 weight to about -jL of the rosin used, is added, and the mass thoroughly stirred. 

 A tablespoonful of the liquid is now dipped out and immersed for several minutes 

 in a bucket of water at the temperature of the polishing room, which should be 

 about 68° Fahi'enheifc. The si)oonful of rosin is now taken out, and its hardness tried 

 with the thumb-nail. If the rosin is brittle at the thin edges it is still too hard, and 

 a little more turpentine must be added; if, however, it is soft like wa.\ or gum, it is 

 too soft, in which case the pan of rosin must be hardened by boiling for a few min- 

 utes ; this drives off the excess of turpentine. When the rosin is of the proper hard- 

 ness an indentation about ^ inch long can be made in it by moderate pressure of the 

 thumb-nail for five seconds. When the proper degree of hardness has been ob- 

 tained it is often necessary to heat the pan of I'osin again so that it will not be too 

 thick to pass readily throtigh the strainer; this is a long, narrow bag of cheese- 

 cloth through which the rosin is strained as it is being poured into the grooves or 

 moulds previously described. If such heating is necessary it raiist be done gently 

 and without boiling; otherwise the rosin will be hardened. Enough is poured 

 into each groove to just fill it. 



After being poured, the I'osin should cool for six oi- eight hours. Then the 

 nails which held the quarter-inch strips of \vood to the boai'd below are removed, 

 and the layer of rosin, wooden strips, and paper is carefully lifted from the board, 

 when the paper is easily stripped from the rosin, to which it does not adhere 

 closely. With care the thin sti'ips of wood can now be removed, one after the 

 other, and the long strips of rosin, 1:^ inches wide and |- inch thick, are secured 

 without chipping or breaking. These are now readily cut into squares with a 

 hot knife. 



The squares are attached to the previously marked wooden basis by quickly 

 warming one face of each square over a flame and then pressing it gently ao^ainst 

 the tool with the fingers. The tool is now ready for rough-pressing. 



Three strong eyes are screwed into the back of the tool, and it is suspended, 

 face down (by means of wires connected to the ceiling of the room), so as to hau<i- 



