480 Prof. W. F. Barrett. On the Increase of Electrical 



broad bands by absorption. I have never expressed the opinion, 

 that the disappearance of the light between the D-lines in the absorp- 

 tion spectrum of dense sodium vapour is only a result of the strong 

 dispersion ; but I warned against always ascribing the observed dark 

 bands to absorption only. 



Wood's recent researches are very important as a contribution to 

 our knowledge of dispersion in general. For the present their bearing 

 on the spectral phenomena exhibited by the light from the chromo- 

 sphere and from sun-spots, seems not to be so direct, because, most 

 probably, the density of the vapours is much less in the solar atmo- 

 sphere than in the dispersion tubes used by "Wood in his brilliant 

 experiments. 



i( On the Increase of Electrical Resistivity caused by Alloying 

 Iron with Various Elements, and the Specific Heat of those 

 Elements." By W. F. BARRETT, F.R.S., Professor of Experi- 

 mental Physics in the Royal College of Science for Ireland. 

 Received December 16, 1901 Read February 6, 1902. 



In the following note I wish to draw attention to a connection which 

 appears to exist between the electric conductivity of certain alloys of 

 iron and the specific heats, and hence atomic masses, of the particular 

 elements with which the iron is alloyed. In a paper published in the 

 ' Transactions ' of the Royal Dublin Society the electric conductivity 

 and magnetic permeability of a very large and, I believe, unique 

 collection of alloys of iron is given.* These alloys, it may be men- 

 tioned, have been prepared with great care by my friend, Mr. R. A. 

 Hadfield, Managing Director of the Hecla Steel Works, Sheffield. Of 

 the alloys made, 110 different specimens were found homogeneous, and 

 could be forged and rolled these were analysed at the Hecla works, 

 and submitted to similar heat treatment all being carefully annealed 

 under the direction of Mr. Hadfield. 



The specimens were in the form of rods, of nearly circular cross- 

 section, about one-half a centimetre in diameter and 104 cms. long. The 

 conductivities were found by the potential method, a standard of pure 

 copper being employed. Although the determination of the mean 

 sectional area of the specimens was made with great care, by numerous 

 measurements of each rod with a micrometer screw, and also by means 

 of water displacement, yet, owing to slight irregularities in the 

 diameters of the rods, and the numerical importance of this value in 



* " On the Electrical Conductivity and Magnetic Permeability of Various 

 Alloys of Iron," by W. F. Barrett, F.E.S., W. Brown, B.Sc., and R. A. Hadfield, 

 M.Inst. C.E., 'Trans. Royal Dublin Society,' January, 1900. 



