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Art. XVI. MISCELLANEOUS INTELLIGENCE. 



I. Mechanical Science. 



1 . Dr. Black's Sensible Balance. — The following description of 

 a very delicate and, to many it may be, very useful balance, is 

 taken from a letter written by Dr. Black, to James Smithson, 

 Esq., and inserted in the Annals of Philosophy, N. S. x. 52. " The 

 apparatus I use for weighing small globules of metals, or the 

 like, is as follows : A thin piece of fir-wood, not thicker than a 

 shilling, and a foot long, 3-10ths of an inch broad at the middle, 

 and lj tenths at each end, is divided by transverse lines into 20 

 parts, i. e. ten parts on each side of the middle. These are the 

 principal divisions, and each of them is subdivided into halves 

 and quarters. Across the middle is fixed one of the smallest 

 needles I could procure, to serve as an axis, and it is fixed in its 

 place by means of a little sealing-wax. The numerations of the 

 divisions is from the middle to each end of the beam. The ful- 

 crum is a bit of plate-brass, the middle of which lies flat on my 

 table when I use the balance, and the two ends are bent up to a 

 right angle, so as to stand upright. These two ends are ground 

 at the same time on a flat hone, that the extreme surfaces of them 

 may be in the same plane ; and their distance is such that the, 

 needle, when laid across them, rests on them at a small distance 

 from the sides of the beam. They rise above the surface of the 

 table only one and a half or two-tenths of an inch, so that the 

 beam is very limited in its play. 



«' The weights I use are one globule of gold, which weighs one 

 grain, and two or three others which weigh one-tenth of a grain 

 each ; and also a number of small rings of fine brass wire, made 

 in the manner first mentioned by Mr. Lewis, by appending a weight 

 to the wire, and coiling it with the tension of that weight round a 

 thicker brass wire in a close spiral, after which the extremity of 

 the spiral being tied hard with waxed thread, I put the covered 

 wire in a vice, and applying a sharp knife, which is struck with a 

 hammer, I cut through a great number of the coils at one stroke, 

 and find them as exactly equal to one another as can be desired. 

 Those I use happen to be the one-thirtieth part of a grain each, or 

 300 of them weigh ten grains ; but I have others much lighter. 



" You will perceive that by means of these weights, placed on 

 differents parts of the beam, I can learn the weight of any little 

 mass, from one grain, or a little more, to the -j? 1 ^ of a grain. For 

 if the thing to be weighed weighs one grain, it will, when placed 

 on one extremity of the beam, counterpoise the large gold weight 

 at the other extremity. If it weighs half a grain, it will counter- 

 poise the heavy gold weight at five ; if it weighs 6-10ths of a 

 Vol. XX. M 



