30 PROFESSOR C. V. BOYS ON THE 
finally gently beaten in the mould. These balls were made in pairs, identical in 
weight, so far as I could determine with the balance. The smallest weighed 
1:'2983 grams each. The point of a fine needle, held in a special tool in which the 
ball was placed, was forced a short way into the gold, and removed, after which the 
ball was replaced in the dies and compressed again, which process forced down the 
very small elevation round the little hole, and left a much smaller hole than could be 
made direct. In order to fasten these balls to their respective fibres, a pin was 
dipped in shellac varnish and rapidly passed across the end of the fibre. After one 
or two trials, a semi-microscopie bead of varnish, formed by capillarity, was left just 
above the end of the fibre. This was then placed in the little hole in the ball, and 
the latter was placed in a conical hole in a brass blank, which had been warmed in 
the flame of a spirit lamp. Under the influence of the warmth the little bead slid 
down, and instantly flashed into vapour as it touched the gold ball. If necessary, a 
small quantity more varnish could be applied upon the point of a very fine needle. 
The ball thus attached formed the lower part of a perfect Borda pendulum, there 
being nothing visible outside the spherical surface. So perfect is this mode of support 
that when a gold ball is hung up by its fibre, and set in torsional vibration, the image 
ot the window seen reflected on the spherical surface was not seen to move or quiver 
when examined by a strong lens. The upper end of the fibre was fastened with 
shellac to the tail of the hook and eye, seen in fig. 7, the length of course being 
adjusted so that the gold and lead ball would hang at the same level. 
There is no question that this is the most perfect method of holding the gold balls, 
but when I came to the larger size of -25 inch, weighing 2°6501 grams, the risk 
of fracture due to an accidental roll of the ball was increased, and in one case, after 
a week spent in making all the preliminary measurements, one of the balls drew off, 
owing to imperfectly dried varnish, and it and its companion and the mirror were all 
precipitated down the central tube and the torsion fibre was lost. To reduce the 
risk, I therefore arranged another process which is practically as good and is much 
safer. A piece of No. 40 copper wire, 3 inch long, weighing *00084 gram, was 
inserted into the hole, and soldered in its place with a scarcely visible amount of 
solder, the wire and solder weighing exactly 001 eram. A calculation of the total 
attraction of ball and wire, on the supposition that the wire as well as the ball acts 
upon the centre of the lead ball as if it were concentrated at the centre of the gold 
ball, shows the error to be only ssgae of the whole, it is therefore of no consequence. 
To the side of this wire the quartz fibre was easily fastened with shellac varnish, the 
amount of shellac used being 0001 gram, or even less. I have not made any balls 
of the largest size, but in the one experiment in which larger masses were employed, 
have made instead cylinders of gold, 4 inch in diameter and ‘2587 inch long. These 
were prepared in a similar manner. Mr. CoLeBRooK made for me a hardened steel 
cylindrical mould, the inside being lapped out to size and polished. The end was 
made plane and truly perpendicular to the cylindrical hollow. A polished steel plane 
