}finimtim Pecnxtion tJtroin/h a Prism. 697 



in fio-. G show the results obtained by heatino- a nickel wire 

 •14 mm. diameter which had nor been annealed. 



Experiment Y.— The Effect of Wtriations of Temperature 

 on the C/ianae of Resistance in Iron. 



Two specimens of iron wire were tried. They were botli 

 of -S'i mm. diameter and taken from the same reel ; but one 

 had been hardened by stretchincr nearly to the breakincr- 

 point. The results obtained are shown in fig. 7. 



Experiment VI. — The Effect of Variations of Temperature 

 on the Change of Resistance in Platinite. 



The wire used was the same as that used in the stress 

 experiments, but w^as annealed by heating in the flame. The 

 results obtained are shown by the dotted curve in fig. 5. 

 The change of resistance at 100° C. exhibits a decided 

 maximum^'at a field of about 350 C.G.S., the effect being 

 smaller at higher fields. 



All the experiments described above were carried out in 

 the Physical Laboratoi-y of the University College of North 

 AVales \ and 1 desire to express my best thanks to Prof. 

 Tavlor Jones for placing the necessary apparatus at my 

 disposal, and also for much valuable help and advice given in 

 the course of the work. 



Bangor, Sept. 1903. \ 



LXXXYI. ^' Minimum Deviation through a Prism." 

 By T. L. Bexnett *. 



Sin ^=/x sin ^'. Sin<^ = fisin 0'. 



IN a note under the above title in the Philosophical 

 Magazine for October, it is tacitly assumed that if 

 /i, and (0' + <^') be constants, then n is constant. 

 This is not the case, for 



/xsin(^' + <^') 

 n = — . — -75 r-- . 



sni (^ + 0) 



Thus the deduction a'^= maximum fails. 

 * Communicated by the .Vuthor. 



