A Substitute for the Position Micrometer. 447 



A SUBSTITUTE FOE, THE POSITION" MICROMETER. 



BY CHAELES GEOVEE. 



[A strong interest attaches to the pursuit of science under 

 considerable difficulties, and we therefore depart from our 

 usual custom by saying a few words on the author of this com- 

 munication. He is an artizan — a brushmaker — fortunately 

 possessed of a two-inch telescope, and doing such good work 

 with it as to have attracted honourable notice from Dr. Lee, of 

 Hartwell House, Mr. Birt, and our own highly-esteemed con- 

 tributor, the Rev. T. W. Webb, by whom this paper has been 

 sent to us. The plan adopted by Mr. Grover is certainly 

 ingenious, and may suggest to others, who, like him, cannot 

 afford more perfect instruments, how much may be accom- 

 plished by ingenuity and perseverance. If a poor working 

 man, subsisting and keeping a family upon slender weekly 

 wages, can manage to make considerable progress in observa- 

 tional astronomy by the diligent employment of his leisure 

 hours, what a wide field is open to those who can devote ample 

 time and money to any favourite pursuit ? — Ed.] 



I have been greatly interested in observing the various 

 double and binary stars, so ably treated of in your pages by the 

 Rev. T. W. Webb, and have often wished (as I dare say many 

 other amateurs have done) for some cheap and simple instru- 

 ment for measuring their angular positions, that excellent 

 instrument, the position micrometer, being, from its price, 

 inaccessible to me. 



After a good deal of thought, and the advice of one or 

 two astronomical friends, I have devised and constructed an 

 apparatus which on trial I found so useful that I have thought 

 it worth while to send you a description of it, hoping it may 

 prove acceptable to many of your astronomical readers. 



The first thing to be done is to prepare a carefully-divided 

 circle, of a size corresponding to the eye-end of your telescope. 

 This may be of any suitable material, to suit the amateur's 

 convenience. Mine is simply drawn on paper, and attached 

 to the telescope with a little warm glue. If the telescope is 

 of small diameter, the circle may be of larger size, so as to 

 project all round; but then it becomes liable to be injured by 

 contact with various objects. 



As to dividing, large circles have the advantage of small 

 ones, in giving more space for division, and crowded circles 

 are difficult to read by the faint light allowed in the observing- 

 room. Mine is but two inches in diameter — a size not large 

 enough to allow of single degrees being shown on it well ; 



