MISCELLANEOUS PAPERS. 361 



in the usual equatorial style, with right ascension and declination cir- 

 cles and adjusting rods, but without a driving clock and other costly- 

 attachments, can be secured for about $500. Such an instrument 

 would bear, with ease, powers ranging from 100 to 500 diameters — a 

 range ample for all practical purposes. When freshly resilvered, 

 this glass would bear a power of 1000. The mounting of such an in- 

 strument in a neat observatory need not cost more than $500, and 

 might be brought within $250. The total cost, therefore, need not be 

 more than $750 to $1000. This is not beyond the reach of any mod- 

 erately thriving educational institution ; and yet how few of them have 

 anything approaching such an equipment ? Indeed, not longer ago 

 than three years, there was not a single such instrument in the state, 

 and but few telescopes of even moderate pretensions. 



The care of such a telescope is not beyond the person of average 

 ability and training. The glass should, of course, be protected by a 

 dust-proof covering of oilcloth or tarpaulin, and, in addition, the open 

 end and eyepiece tube should be securely capped. If carefully pro- 

 tected in this manner, it would be advisable to let the telescope rest 

 in a vertical position, so that the mirror may lie flat, thus avoiding- 

 unnecessary strain in the intervals of usage. 



A tarnished mirror may sometimes be brightened by rubbing it 

 lightly with a soft chamois skin padded with cotton. A good silver 

 surface can be repolished several times. Sometimes, a little rouge 

 upon the pad will aid in polishing. If this does not suffice, the mir- 

 ror must be resilvered. If the glass is sent away, resilvering and 

 repolishing a twelve-inch mirror will cost about ten dollars, and pro- 

 portionately for other sizes. If the work is done in the home labora- 

 tory, the materials need not cost over fifty cents, and the whole 

 operation can be completed in a half-day. It is better to have the 

 reagents prepared before beginning with the mirror. The directions 

 given below are for a twelve-inch glass, following the process given 

 by Doctor Brashear, of Allegheny, Pa. 



Reducing Sohition (prepare at least a week before using; the 

 solution improves with age): 2^ oz. white sugar or rock candy; ^^ 

 oz. nitric acid; 3j oz. alcohol; 19 oz. distilled water. Mix, and keep 

 in a well- stoppered bottle. This solution will be sufficient for several 

 operations. 



DIRECTIONS FOR SILVERING A TWELVE-INCH MIRROR. 



Reagents: -f^ oz. potassium hydroxide, dissolved in about 13 oz. dis- 

 tilled water ; 3% oz. silver nitrate, dissolved in 13 oz. distilled water 

 (reserve about one-sixth of the silver nitrate for later use); a half 

 pint of dilute (about 25 per cent.) ammonia ; a* bottle of dilute nitric 

 acid. Too much care cannot be taken to have pure reagents. The 



