12 The Ohio Journal of Science [Vol. XVI, No. 1, 



delicate such lapping must be. For this work the lap is covered 

 with pitch which has been brought to the proper degree of 

 hardness either by boiling, to harden it or by adding asfalt 

 varnish to soften it. The proper degree of hardness is very 

 important and must be adjusted to the temperature of the 

 room. Obviously if the pitch is too soft it will not hold its 

 shape and it will be impossible to hold the polishing tool to the 

 proper radius. I have put three different curves on a lens 

 about an inch in diameter in a few minutes and it had to go 

 back on the grinding machine before it could be finished. 



The polishing tool is prepared as follows: A disk of pitch, 

 about 3^" thick, is cast by pouring it in a mold made by a 

 strip of brass bent to a circle, the ends clamped w^th a tool 

 maker's clamp, and rested on a piece of cold cast iron which 

 has been planed smooth. This should be of such size that when 

 bent to the proper shape it can be molded over a tool similar to 

 the grinding tool but with a radius changed by about the 

 thickness of the pitch. This tool is then heated and painted 

 with a stick of pitch, the disk is warmed, and the two pressed 

 together, when cooled the pitch will stick tight to the iron but 

 will be far from a smooth surface. This and the master tool of 

 the opposite curvature are placed in warm water and pressed 

 together and at the same time one slowly rotated, one about the 

 other. When a good fit is secured they are cooled and a number 

 of small holes, about 1-8" in diameter, are drilled all over the 

 pitch to distribute the abrasive, which of course spoils the sur- 

 face and the tool must be again pressed. This pressing to shape 

 must be done repeatedly and requires great care and some 

 practice in order to have the pitch come to the exact opposite 

 of the pressing tool. The most important thing is to do the 

 pressing slowly and in fact in the whole process of this work 

 one must never get in a hurry. Ritchey, in his memoir on the 

 construction of the great 60" at Mt. Wilson, recommends cov- 

 ering the pitch with beeswax, and for quicker and poorer work 

 a cloth polisher may be used, the cloth being a special felt and 

 cemented to the cast iron tool with a thin layer of pitch. 



The abrasive is rouge or red oxide of iron and its preparation 

 is fully described in the above mentioned work by Ritchey. We 

 purchased the anhydrous red oxide of iron from Merck & Co. 

 This was mixed with plenty of water in the jars shown at E, 

 Fig. 5. The rouge will rapidly precipitate, the coarse particles 



