10 THE MODERN REFLECTm& TELESCOl'E. 



about two feet above the flame of a gas or gasoline stove. The tool can now be 

 swung about so that the rosin squares are warmed unifoi'mly. Wiien the squares 

 are slightly soft and very slightly warm, htif not Itot, to the touch, the tool is 

 placed upon the previously ground glass which is to be polished, the glass having 

 just previously been thoroughlj' wet with distilled water so that the rosin will not 

 stick to it. Slight pressure may be exerted to assist in pressing the rosin surface 

 to fit the glass. The tool will have to be slightly warmed and piessed several times 

 befoi-e good contact is secured all ovei'. I always prefer to " rough-press " the rosin 

 tools on an iron grinding tool having the same form as the glass, if a sufficiently large 

 one is available; but the precaution is always taken to cover the iron tool with 

 clean wet paper. 



The I'osin squares will have spread somewhat irreguhii'ly during the longli- 

 pressing ; so the surface is marked with a straight-edge and knife, and the edges of 

 the squares are trimmed so that the grooves between them are straight and of iini- 

 form width. This trimming is best done with a sharp knife, held so as to make an 

 angle of about 60"^ with the surface of the tool, and drawn quickly toward the 

 workman. 



The rosin squares are now ready for coating with wax. A pound of best bees- 

 wax is melted in a large clean cup and is very carefully strained through sevei'al 

 thicknesses of cheese-cloth into a similar clean cup. A brush is made by tying sev- 

 eral thicknesses of cheese-cloth around theeml of a tliin blade of wood 1^ inches wide. 

 Each rosin square is now coated with a thin layer of wax, by a single stroke of the 

 brush; the wax should be very hot, otherwise the la3rer will be too thick. 



The tool is now ready for "cold-pressing" or "fine-pressing," a matter of the 

 most vital impoi'tance, whicli will be more propei-ly described latei", in connection 

 with the work of polishing the glass. 



The work of making a large concav'e mirp)r will now be described in detail. 



CHAPTER VI. 



ROUGH-GRINDING THE FACE AND BACK OF A ROUGH DISK OF GLASS, AND 



MAKING THE SAME PARALLEL. 



The rough disk of glass is placed upon the cai'peted turntable, and a long 

 strip of thin oilcloth is drawn around its edge; the upper edge of the oilcloth is 

 securely fastened to the glass by means of a strong cord, and the junction between 

 oilcloth and glass is made water-tight by means of water-proof adhesive tape. The 

 oilcloth strip is wide enough to hang several inches below the edge of the iron 

 plate on which the glass rests, so that the cii'cular trough of galvanized iron, which 

 can lie seen in Plates rv and vi, catches all of the emery and water which are 

 washed over the edcres of the crlass durinof iri'indincr ; this circular troug^h is station- 

 ary, has two holes in its bottom above the buckets, which can be seen in the plates. 



