472 [March 12, 



although it is less marked than in the case of the hollow cylinders, 

 as might have been expected. 



The tendency of the cooled skin of a heated metallic mass to 

 squeeze out its contents appears to be what gives rise to the bulging 

 seen near the water-line in the hollow cylinder of brass. Wrought 

 iron, being highly tenacious even at a comparatively high tempera- 

 ture, resists with great force the sliding motion of the particles which 

 must take place in order that the tendency of the cooled skin to 

 squeeze out its contents may take effect ; but brass, approaching in 

 its hotter parts more nearly to the state of a molten mass, exhibits 

 the effect more strongly. It seems probable that even in the case of 

 brass a very thin hollow cylinder would exhibit a contraction just 

 above the water-line. Should there be a metal or alloy which about 

 the temperatures with which we have to deal was stronger hot than 

 cold, the effect of the cause first referred to would be to produce an 

 expansion a little below the water-line. G. G. S.] 



March 12, 1863. 



Dr. WILLIAM ALLEN MILLER, Treasurer and Vice- 

 President, in the Chair. 



His Grace the Archbishop of York was admitted into the Society. 

 The following communications were read : 



I. " On the Influence of Temperature on the Electric Conduct- 

 ing Power of Thallium and Iron/' By A. MATTHIESSEN, 

 F.R.S., and C. VOGT, Ph.D. Received February 12, 



1863. 



(Abstract.) 



Thallium. The experiments detailed in this paper were made 

 with specimens of thallium lent to us by Mr. Crookes and Proiessor 

 Lamy of Lille. The values obtained for the conducting power, 

 together with the formulae for the correction of the conducting 

 power for temperature of the different specimens, were : 

 For Mr. Crookes' s metal, 



1st wire. 2nd wire at 0. 



9'169. 



