1831 .] 
Accurate Balances. 
223 
provided with a drawer, opening from behind, into which the substances weighed 
were deposited, through a small spring trap-door in the floor of the case, to prevent 
their incumbering the case. The dimensions of the pedestal were 20 inches by 16, 
and 5£ inches high ; the total height of the case was 30 inches, and the whole expense 
of construction, by native workmen, both of balance and case, was 158 Rupees. 
As some apology may be due to your readers, for troubling them with so detail- 
ed a description of a balance made for my own purposes, and not likely to come into 
general use, I will, in conclusion, show how much more simple means maybe 
applied to attain nearly an equal degree of accuracy, by extracting Doctor 
Black’s account of a “ very Sensible Balance” from the Annals of Philosophy, for 
1825. It is represented in Plate XII. fig. 16. 
“ A thin piece of fir wood, not thicker than a shilling, and a foot long, three- 
tenths of an inch broad in the middle, and one-tenth and a half at each end, is di- 
vided by transverse lines into twenty parts ; that is, 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 numeration of the divisions is from the middle to each end of the beam. 
The fulcrum 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 ex- 
treme surfaces of them may be in the same plane ; and their distance is such that 
flic needle, when laid across them, rests on them at a small distance from the sides 
ot the beam. They rise above the surface of the table only one-tenth and a half or 
two-tenths of an inch, so that the beam is very limited in its play : — see fig. 190. 
‘ I lie 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 ap- 
pending a weight to the wire, and coiling it with the tension of that weight round 
a dicker brass wire in a close spiral, after which, the extremity of the spiral being 
bed hard with waxed thread, I put the covered wire into a vice, and applying a 
f’h.irp knife, which is struck with a hammer, I cut through a great number of the 
Cods at one stroke, and find them as exactly equal to one another as can be de- 
Slrcd - Those I use happen to be the ^th part of a grain each, or 300 of them 
"eigh ten grains ; but I have others much lighter. 
^ ou will perceive, that by means of these weights, placed on different parts of 
the beam, I can learn the weight of any little mass from one grain, or a little more, 
to tlie issgth of a grain. For if the thing to be weighed weighs one grain, it will, 
"hen placed on one extremity of the beam, counterpoise the large gold weight at 
the other extremity. If it weighs half a grain, it will counterpoise the heavy gold 
weight placed at 5. If it weigh T s n thsof a grain, you must place the heavy gold weight 
fi t 5, and one of the lighter ones at the extremity to counterpoise it ; and if it weighs 
0l ‘H one or two, or three or four hundredths of a grain, it will be counterpoised by 
° nc ^e small gold weights placed at the first or second, or third or fourth divi- 
Slon - If, on the contrary, it weighs one grain and a fraction, it will be counterpois- 
Cd ^ the heavy gold weight at the extremity, and one or more of the lighter ones 
P ^ced in some other part of the beam. 
I his beam has served me hitherto for every purpose; but had I occasion 
0r a more delicate one, I could make it easily, by taking a much thinner and 
l, 'hter slip of wood, and grinding the needle to give it an edge. It would also 
be 
eas y to make it carry small scales of paper for particular purposes. 
P. 
