42 Mr. \V. Galloway. On the [May 15, 



the angles of incidence being taken as abscissae, and the intensities as 

 onliimtes; those representing the calculated intensities being drawn 

 with dotted lines. 



The inequalities in that for the observed value with light polarised 

 in the plane of incidence, and the thin silver film (Fig. la) would 

 probably have disappeared if a larger number of observations had 

 been made, the curve for the calculated value, however, corresponds 

 very nearly with the line which would have been obtained had a 

 smooth curve been drawn between the points given by observation. 



Fig. 16 gives the results with the thick silver film. 



Figs. II and III represent the observations made with the steel* 

 and speculum metal mirrors. (" Proc. Roy. Soc.," vol. 36, p. 187.) 



These diagrams appear to confirm the general conclusion arrived at 

 in the former paper, that although the received formulae for metallic 

 reflection are approximately correct, they are not a complete expres- 

 sion of the facts of the case. 



EXPLANATION OF DIAGRAMS. 



la. Amount of light reflected by silver film. 



16. Amount of light reflected by double silver film. 



II. Amount of light reflected by steel mirror. 



III. Amount of light reflected by speculum metal mirror. 



A. Light polarised in the plane of incidence. Observed. 



B. Calculated. 



c. ,, perpendicularly to the plane of incidence. Observed. 



D. Calculated. 



II. " On the Influence of Coal-Dust in Colliery Explosions. 

 No. V." By W. GALLOWAY. Communicated by R. H. SCOTT, 

 F.R.S. Received May 8, 1884. 



At the beginning of the first paper on this subject, which I had the 

 honour of reading before the Fellows of the Royal Society now some- 

 what more than eight years ago (" Proc. Roy. Soc.," vol. 24, p. 354), 

 I gave a short account of what appeared to me to be a rational mode 

 of explaining the occurrence of all great explosions in dry and dusty 

 collieries ; and since then I have had opportunities of studying several 

 remarkable instances of this class of phenomena, with the result that 

 I am now more than ever satisfied with the correctness of the views 

 which I then expressed. It is true, as some subsequent writers, 

 amongst whom I may name Sir Frederick Abel, F.R.S., have 

 observed, that coal-dust had been previously recognised as a factor in 



The yalue of I 1 for steel at an angle of 60 is 46 14', and not 42 09 7 , as given 

 in the table on p. 196, an error for which, I regret to say, I am responsible. 



