145 
Ordinary Meeting, March 20th, 1866. 
E. Schunck, Ph.D., F.R.S., Vice-President, in the Chair. 
Mr. John Patterson was elected an Ordinary Member of 
the Society. 
Dr. J. P. Joule, F.R.S., exhibited a balance which he 
had constructed on the principle which had been introduced 
by Professor Thomson, and employed by him in weighings 
for a long time. The adjoining figure will fully explain the 
instrument. The beam has a leaden weight let into its 
extremity b. It is supported by a wire a a stretched between 
the sides of the box containing the balance. This wire is 
led round so as to form the suspender a a of the scale. Silk 
threads c c, c c, hanging from the cross pieces, form a gimbal 
system by which the scale is supported in such a manner 
that any variation in the position of the weights does not 
alter the torsion of the suspender. A counterpoise of known 
weight is placed on the stage d. When an article is to be 
weighed it is placed in the lower part of the scale s, and then, 
the counterpoise being removed, weights are placed on the 
stage to effect the counterpoise in the new condition. The 
difference between the first and second counterpoises of 
course gives the weight required. The upper edge of the 
beam is furnished with an index for showing minute effects ; 
and attached to this is a small bottle e for holding shot or 
sand, by the addition of which the stability of the beam may 
be decreased to any required extent. The instrument exhi- 
• bited was able to weigh articles of upwards of 3,000 grains 
to one hundredth of a grain. Dr. Joule stated that he had 
also employed Professor Thomson’s principle in the construc- 
Pkoceedings— Lit. & Phil. Society.— Vol. V.— No. 13— Session 1865-6. 
