194 C. Barns — Energy Potentialized in Permanent 



Now it is clear that the strain -effect of a given amount of 

 work done must depend on the dimensions of the material. It 

 must be supposed variable with the extension produced in case 

 of a given sectional area, as well as with the section of the 

 stretched wire in case of a given extension. At the outset it is 

 difficult even to conjecture in what respect these strains, though 

 of a given class, may differ in essential details. There is, how- 

 ever, a more interesting phase of these experiments : the strain- 

 effect of a given amount of work done on centimeters of wire 

 will vary, cset. par., with the material acted upon. From this 

 point of view the prosecution of the present research promises 

 to lead to results bearing directly on the nature (form and mu- 

 tual relations) of the molecules sustaining strain. 



2. In figure 1, CC CO, the weights (P=40 kg to 60 kg) by 

 which stretching is to be done 

 are supported on a suitable trap- 

 door, BB ; and the fall of BB, 

 when released, is guided by the 

 upright slides s$, s's', fixed in the 

 firm base, G, of the apparatus. 

 I took pains to adjust the soft 

 wire ah to be acted on, as nearly £. 

 straight and free from initial 

 tensile strain as possible. It was 

 firmly fastened above to a heavy 

 cross-timber of wood, BB, the 

 lintel of a framework which in 

 form and purpose closely resem- 

 bled a gallows. The screw clamp 

 at a in the vertically adjustible 

 brass torsion-circle A, the axle 

 of which passes snugly through 

 BB, secures the upper end of 

 the wire. The lower end is 

 lapped around the hook of the 

 weight pan, bnn, then wound 

 around the wire and soldered, 

 care being taken to a^oid such 

 loops and kinks as might change 

 form during stretching. 



A thermo-couple, aflad, originally of platinum/platinum-irid- 

 ium, with its junction /? tied on with silk thread on the upper 

 half of the wire db, enabled me to measure the change of tem- 

 perature due to stretching. In later experiments more reliable 

 devices were adopted, cf. § 5. Changes of length were measured 

 with Grunow's cathetometer, two fiducial marks having been 

 painted on the wire ah about 70 om apart. At a given signal the 



