«2 



HKPOKT — 1888. 



of the bridge wire in Chrystal's observations was only determined approxi- 

 mately as "075 B.A.U. In this way we get the following Table VI. 



Table VI. 



On examining these differences it would seem that A has changed 

 ^eatly, while B has remained unaltered. This is not in accordance with 

 the conclusions derived from Table V., and will require further considera- 

 tion. With regard to the otter four coils, the differences are almost 

 within errors of observation and are in fair agreement with Table V. 

 Coil C appears to have risen relative to G by '00027 ; thus, since its tem- 

 perature coefficient is "00071, this would correspond to an apparent fall 

 in the temperature at which it is right of about 0°'3 Centigrade. Table V. 

 shows that there has been a fall in this temperature of 0°'2. 



The temperature coefficients of D and B are about "00308, so that the 

 differences recorded for these coils would be accounted for by an error 

 of 0"! in the temperature, while the change in F relative to G is so small 

 as to be within the experimental errors. We are thus led to infer that, 

 while C may have risen slightly, the others have not changed by any but 

 a very small amount. This conclusion as regards F is at variance with 

 the one derived from Table V. In fact, while at 10° F is above G in 

 value ; owing to the small temperature coefficient used by Chrystal for F, 

 its curve of resistance crosses that of G, and at temperatures near 18°, at 

 whicb G is about right, F is considerably below it. 



If we take Chrystal's value for F at 10° and the temperature co- 

 efficient '00026 instead of "00021 used by him, we find that F would be 

 right at about 17°"6 instead of at 19°"4, as given by Chrystal. This is 

 much closer to 16°'9, the value given by our observations ; if we take it 

 instead of the 19-4 of Table I., the results of this Table VI. and of Table V. 

 would point to a rise in the value of F of about "00017. 



The conclusion then that would seem to follow from a comparison of 

 these two series of observations in 1876 and 1888 would seem to be that, 

 while considerable uncertainty attaches to the coils A and B, changes 

 in the other five coils, C, D, B, F, and G, if they have occurred at all, 

 are probably not so great as "0002 B.A. Unit. C and F may possibly 

 have risen by this amount, while D, B, and G have not varied at all. 



Professor Chrystal's observations in 1876 are in accordance with those 

 of Messrs. Matthiessen and Hockin in 186-4! and 1867, while the results of 

 Dr. Fleming's work in 1880 agree, as we have seen, with our own at the 

 present date. 



The observations recorded and discussed above were made mostly at 

 temperatures between 10° and 20°. A considerable number more were 

 made during the cold weather in January and February of the present 

 jear at temperatures near 0°, and we must now consider them. 



