S/A' WILLIAM SIEMENS, F.R.S. 



409 



tend to float up the brick of solid metal. Dr. Siemens was 

 tltridedly of opinion that the fact of the brick being at a lo\\< r 

 temperature than the metal would cause downward currents, and, 

 tlu iv tore, the mechanical effect of such currents must be to draw 

 the brick itself downwards rather than upwards. But there was 

 one cause Mr. Bell had not mentioned, -which he thought might 

 have considerable influence in producing flotation. In pushing a 

 mass of iron below fluid metal, it began to heat on the surface, 

 and consequently expanded superficially, and that expansion 

 caused a tension on the metal in the interior. From a hurried 

 calculation he found that the amount of heat required on the 

 surface in order to expand the interior mass 1 per cent, was not 

 beyond the limit of what they could expect. Iron expanded, for 

 1 Fahr., 0*000018 of its bulk, and, therefore, it would expand 1 

 per cent, for an increase in temperature of 550 Fahr. This 

 difference of external and internal temperature, in the opinion of 

 Dr. Siemens, would account for the expansion in the interior, and 

 would help them over the difficulty of accounting for the rising of 

 the briquette. The difference of volume was at any rate not so great 

 as to invalidate the theory brought before them by Mr. Wright- 

 son. As regarded the cause of the observed phenomena, it appeared 

 to Dr. Siemens that there was nothing unnatural or improbable iu 

 assuming that metal would change its density at certain points,, 

 accompanied by changes in other physical conditions. As to 

 changes in its physical character, there were other substances to 

 guide them, and they had a remarkable illustration in the metal 

 selenium. That metal had been fully investigated on account of 

 the extraordinary phenomenon it presented of becoming less con- 

 ductive of electricity when under the influence of a ray of light. 

 His brother (Dr. Werner Siemens) had examined the conditions 

 under which this change took place, and he found that when 

 selenium was allowed to cool gradually, it suddenly at a certain 

 point changed its capacity for heat. The thermometer which 

 dropped in a uniform ratio until this critical point was reached, 

 suddenly rose, showing that the selenium at that point parted 

 with a considerable quantity of latent heat. He believed that if 

 Mr. Wrightson could extend his experiments to thermometrical 

 measurement of an accurate kind, he would find that cast iron 

 when it began to expand absorbed a great deal of heat which 



