1S4 I'1-..f. A. ' ir.iv. Mr. V. .1. r.lytl,. aii.l Mi. .1. S. Dunl-.j,. 



junction ( 1) J5 cm. al>ove the lower end <.f the jacket. An arrange- 

 ment of mercury cups enables any of the thermal junctions to lie 

 brought into the circuit of the galvanometer and the cold junction. 

 1 is of course taken to ensure that the wires leading from the junc- 

 tions to the galvanometer are never in contact with the inner wall of 

 the heating jackef or with the wire. 



Each thermo-electric couple before use, and from time to time after- 

 wards, was carefully calibrated in the usual way by comparison with 

 thermometers plared with the junctions in water, the temperature 

 of which could be conveniently altered through the range over which 

 the experiments extended. The results were expressed in curves from 

 which the temperatures of the junctions were obtained in the experi- 

 ments. The sensitiveness of the galvanometer was such as to give 

 alxnit eight divisions deflection per degree of difference of temperature. 

 This arrangement worked satisfactorily ; but in future experiments it 

 will probably le replaced by a platinum thermometer. 



nf YHIHI v'x Mul ill n.<. 



Experiments were made for each wire, first as to the variation of 

 Young's modulus with temperature, next as to the variation of the 

 rigidity modulus with temperature, and, in connection with this latter 

 determination in each case, of the rate of dying out at the different 

 temperatures of torsional oscillations. The results of the last-men- 

 tioned observations are, we think, very interesting, but we give here 

 in the first place the information obtained with regard to Young's 

 modulus. 



A scale-pan, weighing about 4 Ibs., was attached to the wire and 

 loaded to such an extent as not to produce gradual increase of length 

 of the wire. A small reading-microscope, with a convenient scale in 

 its eye-piece, was rigidly mounted on a heavily loaded table resting on 

 the solid stone floor of the laboratory, and was focussed on the point of 

 a very fine needle soldered to the wire just below the lower end of the 

 heater. The needle was set so as to be as nearly as possible at the 

 proper end of the scale to give a displacement along the scale when the 

 weight was removed from the wire. A similar arrangement at the 

 upper end served to determine the amount by which the support 

 yielded with different loads. This microscope was supported on a 

 horizontal board firmly attached to two massive roof-girders at a 

 distance from the beam to which the wire was suspended. 



Enough of the load was then removed to cause the needle to traverse 

 nearly the whole length of the scale, and the readings of the top and 

 lottom microscopes were observed. A series of readings for weights 

 on and off were first taken at the ordinary temperature of the room, 

 and again after steam had l>een blown for some time through the heat- 



