Temperature on Modulus of Rigidity of Solid Metals. 409 



the measurement is made, it is very difficult to compare the 

 values obtained by the present experiment with those of 

 other investigators. 



2. Zinc. Fig. 3. 



Since zinc wire is not strong, the lighter lead ring was 

 used. From fig. 3 we see that. owing to the low melting- 

 point of the metal, the rigidity decreases very rapidly with 

 the rise of temperature. The fact that the lower the melting- 

 point the greater is the rate of decrease of rigidity with the 

 rise of temperature, has been already observed by Benton, 

 who investigated the rigidity of copper and steel at tempera- 

 tures between 20° and —186° C. The observed curve 

 seems to form a portion of a parabolic curve. In the same 

 figure the logarithmic decrement temperature curve is 

 given; it rapidly rises with temperature. 



3. Aluminium, Gold, and Silver. Figs. 4, 5, & 6. 



The variation of rigidity of these metals with the rise of 

 temperature is also similar to that of the above metals ; the 

 form of the curves is intermediate between those of copper 

 and zinc. Similar remarks apply also to the logarithmic 

 decrement-temperature curves. 



4. Platinum and Platinum-rhodium. Figs. 7 & 8. 



The platinum wire is obtained from the Leeds & Northrup 

 CJo., Philadelphia, and is of high purity, being the material 

 for the use of the thermoelement. Platinum-rhodium wire 

 contains 15 per cent, of rhodium, and is of an ordinary 

 quality. The course of the rigidity-temperature or logarith- 

 mic decrement-temperature curves for these two wires are 

 similar to each other — that is, with the rise of temperature 

 the diminution of rigidity is at first small, but it gradually 

 increases. Above 500° the diminution is relatively rapid, 

 but even at a high temperature of 750° 0. we still observe 

 a large value of rigidity. The increase of logarithmic 

 decrement with the rise of temperature is at first very slow, 

 but above 400° it increases very rapidly. Some quantitative 

 differences between these wires are, however, to be observed. 

 At ordinary temperatures the rigidity of platinum is a little 

 less than that of platinum-rhodium, but the rate of dimi- 

 nution of the rigidity at high temperatures is for the former 

 metal much less than that of the latter. The logarithmic 

 decrement of platinum is always greater than that of 



