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XII. Account of Experiments on Torsion and Flexure for the Determination of Rigidities. 
—Third Paper. By Joseph David Everett, D.C.L . , Professor of Natural Philo- 
sophy in Queen's College , Belfast. Communicated by Sir William Thomson, F.R.S. 
Received January 13, — Read January 30, 1868. 
These experiments are a continuation of those described in my papers read February 
26th, 1866 and February 7th, 1867. They were made during the Winter Session of 
1866-67, in the same place, and with the same apparatus as the later experiments on 
the steel rod (see p. 150 of last paper), the observer being Mr. Zacciieus Walker, 
student of Engineering, who has been already mentioned as joint observer in the expe- 
riments on the steel rod. I personally inspected the apparatus from time to time, and 
assisted in the taking of those measurements which only required to be made once for 
all in the case of each rod. The weights, in air and water, of the portions of rods ope- 
rated on, were observed by Mr. John Tatlock, Laboratory Assistant to Sir William 
Thomson, who also performed this portion of the labour in the previous experiments. 
The rods operated on in the experiments now to be described w r ere three in number, 
and were of malleable iron, cast iron, and copper respectively, those previously operated 
on being of flint glass (two specimens), brass, and steel. 
Experiments on Malleable Iron Bod. 
The mean values of T (proportional to torsion) and F (proportional to flexure) were 
as follows, the pointer-readings indicating the amounts by which the rod had been 
rotated about its axis from a certain initial position. 
Pointer- 
reading. 
T. 
E. 
Pointer- 
reading. 
T. 
E. 
30° 
210-3 
165-3 
120° 
210-7 
165-0 
60° 
212-0 
164-8 
150° 
210-1 
165-0 
o 
O 
05 
210-3 
165-3 II 
180° 
210-8 
165-2 
Combining, as theory requires, those positions which are mutually at right angles, we 
have — 
From 30° and 120° . . . T=2105 F=165-2 
„ 60° „ 150° . . . „ 211-0 „ 164-9 
„ 90° „ 180° . . . „ 210-6 „ 165-2 
The cross-piece on whose arms the weights are hung, ought to have been turned 
through a right angle in passing from the position 90° to the position 120°, in order to 
MDCCCLXVIII. 3 E 
