166 Prof. W. E. Ayrton and Mr. H. Kilgour. [Nov. 19, 



November 19, 1891. 

 Mr. JOHN EVANS, D.C.L., LL.D., Treasurer, in the Chair. 



Mr. William Anderson and Professor Frederick Orpen Bower were 

 admitted into the Society. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



In pursuance of the Statutes, notice of the ensuing Anniversary 

 Meeting was given from the Chair. 



Sir James Cockle, Mr. F. Galton, and Mr. Stainton were by ballot 

 elected Auditors of the Treasurer's accounts on the part of the 

 Society. 



The following Papers were read : 



I. " The Thermal Emissivity of Thin Wires in Air." By W. E. 

 AYRTON, F.R.S., and H. KILGOUR. Received July 2, 1891. 



(Abstract.) 



In 1884 it was observed experimentally that whereas the electric 

 current required to maintain a thick wire of given material, under 

 given conditions, at a given temperature was approximately pro- 

 portional to the diameter of the wire raised to the power three halves, 

 the current was more nearly proportional to the first power of the 

 diameter if the wire were thin. When this difference in the behaviour 

 of a thick and thin wire was first noticed it was regarded as being 

 quite unexpected. But, as pointed out by one of us in the course of 

 a discussion at a meeting of the Royal Society, the unexpected charac- 

 ter of the result was due to people having assumed that the loss of 

 heat from radiation and convection per square centimetre of surface 

 per 1 excess temperature was a constant, and independent of the size 

 and shape of the cooling body. 



The very valuable investigations that have been made on emissivity 

 by Mr. Macfarlane, Professor Tait, Mr. Crookes, Mr. J. T. Bottomley, 

 and by Mr. Schleiermacher had for their object the determination of 

 the variation of the emissivity with changes of the surface and with 

 change in the density of the gas surrounding the cooling body, but ifc 

 was not part, of these investigations to determine the change in the 



