426 Proceedings of the Royal Society of Edinburgh. [Sess. 
Method of Conducting the Experiment. 
The wire under consideration was suspended from a clamp attached to 
a torsion head, and at the other end was clamped, symmetrically and 
horizontally, a heavy lead ring of large moment of inertia. To the outer 
surface of this ring was fastened a scale divided into millimetres. The 
vibrations of the apparatus were damped out, and the torsion head then 
carefully turned so that no pendulum oscillation should be set up in the 
wire. Exterior disturbances were also, as far as possible, avoided. Readings 
of successive maxima ranges of oscillation were taken by means of a tele- 
scope with cross wires inserted, the crossing point being fixed in the same 
horizontal plane as the lead ring, at a distance of about 6 feet from the 
scale. It was found convenient to miss the first reading, and to take 
readings at the end of every oscillation after the first until ten oscillations 
had been completed, and thereafter to take readings after every fifth 
oscillation. Except in the case of tin wire, in which case the oscillations 
died down with extreme rapidity, the readings were extended over a 
hundred oscillations. The zero of the scale was found by taking successive 
readings to right and left at intervals, and the average of these values was 
then taken. A curve drawn with the scale readings as ordinates and the. 
number of swings as abscissae showed by means of the waviness of the 
curve if ordinary pendulum oscillations had been appreciably started in the 
apparatus. The values of log y were then plotted against those of log (x + a), 
and when the proper value of a had been found, so that the points lay 
practically on a straight line, the constants were obtained. 
Confirmation of the Empirical Law. 
Wires of nine different metals were tested, brass, copper, aluminium, 
tin, zinc, silver, german silver, platinum, and nickel. Of these, brass, tin, 
zinc, silver, german silver, and nickel were found at the ordinary temperature 
to give close agreement, over the very large range of oscillations taken, to 
the general law, in each case a suitable value of a being found which caused 
all the points to lie on a straight line. It was found, however, that in the 
case of the remaining metals, and especially in the cases of aluminium and 
copper, no one value of a could be found to bring all the points into one line, 
an s-shaped curve being obtained in general. When this was first observed, 
it was thought that the law did not hold in such cases, or at least that it 
did not hold over the range taken. In attempting to straighten, in this 
case, one part of the curve, however, it was found that, with a certain value 
of a , the points could be brought to lie on two straight lines inclined at an 
