Lloyd's Fringes for Internal Reflexion. 503 



In sets [A] and (By the frequency was of the order of 40 

 and 100 -*— per second respectively. 



The agreement of sets (A) and (B) appears satisfactory : 

 while the slightly higher result given by I C) is probably 

 within the limits of possible error of the method as used*. 

 The readings in (A] were sensitive to 2 or 3 in 10,Q00. The 

 resistance R was specially wound to avoid capacity and 

 inductance. An inductance or' 0*1000 henry was added in 

 the branch OrO. The total self-inductance of this branch by 

 comparison with our standard inductances was 705 henry. 



Hence, by | 3 >, 



' T / R \ 0*765x100 - -- , i 



M = L -T-- . = — . ^. -— - U-ij.j 1 henrv. 

 Vbt-> ' 1525-5 



which is o-ood agreement with the results given by the 

 formula 



M = lO^KR-r. 



Thus we infer that in the mica condenser used there is no 

 appreciable apparent series resistance such as Rowland and 

 other experimenters found in some cases. 



I would remark that, after using method (A}. I feel 

 confident that it is still capable of much higher accuracy 

 than that shown above. 



In conclusion I would express my best thanks to Lh\ Grlaze- 



brook for most valued advice and help. 



XL VIII. Lloyd's Fringes for Internal Reflexion^ and the Change 

 of Pliose of Ordinarily Reflected Light. By P. V. Sevan, 

 M.A., Fellow of Trinity College, University Demonstrator 

 in Experimented Physics, Cambridgef. 



"Plate XIII." 



I 



T is generally assumed that when light is reflected ex- 

 ternally, as in the applications of the wave theory to 

 Xewton's rings, there is a loss of half an undulation. The 

 evidence for this is the single mirror fringes obtained by 

 Lloyd, and experiments with the three mirrors of Fresnel 

 made by Jamin. In the first case we have interference of 



* The main probable errors in (G) seem to be due to three causes, 

 namely : the variations (natural and other) in the earth's horizontal 

 magnetic lield : some uncertainty in the time measurements : and the 

 magnetizing effect of the current on the galvanometer needles, not 

 necessarily the same for a steady current and a sudden rush, 



f Communicated by the Author. 



