428 Proceedings of the Royal Society of Edinburgh. [Sess. 
straight lines. The following table gives some of the results got with wires 
each one foot long : — 
Best Value of a. 
Value of n. 
Value of b. 
140 
•79 
947 
130 
•76 
765 
120 
•78 
535 
160 
•74 
783 
150 
•79 
1035 
180 
•78 
1242 
From these it is seen that the best value of a in each case lies between 
one and two hundred. Of course, the variations here are explained to some 
extent by the fact that when a reaches this high value, a difference of ten 
or twenty in its value may make very little difference in the closeness with 
which the points tend to lie on one line. In each case the value chosen is 
the mean of these two values which respectively tend to just render the 
curve visibly concave and convex to the origin. The value of n is seen to 
remain practically constant, but the values of b obtained do not seem to 
follow simply any corresponding change in the other constants. 
Effect of Heating. 
After the wire had been heated to redness, a complete change in the 
behaviour when oscillated was experienced. The oscillations died down 
much more rapidly, and it was found that the value of a required fell to the 
neighbourhood of zero, whilst the value of n had greatly increased. It was 
observed, however, as already stated, that the points could not now be fitted 
in to one straight line, but that a value of a could in general be found to 
cause the points to lie along two portions of straight lines.* In a few cases, 
however, two slightly differing values of a were required for the two parts. 
The heating was carried out in an electric furnace, and a series of tempera- 
ture observations carried out to find at what temperature the change from 
a single to a double line occurred, and in what manner the value of n 
changed with increasing temperature. The temperature was measured by 
means of a platinum thermometer and bridge ratio box. It was found 
that the value of n gradually increased with increase of temperature until 
in the region of 300°, when the change became more apparent; n then 
increased rapidly until 375° C., after which two values of n were always 
obtained, which, owing to the value of a being so small, could not be got so 
accurately, the least change in a causing an appreciable difference in the 
* Diagram 3. 
