INDUSTRIAL PROGRESS DURING THE YEAR 187G. Hii 



and in contact with it. The power consumed is measured by a kind 

 of Prony brake arrangement, and the rise of temperature by a ther- 

 mometer placed in mercury in the inner cone. The mean result 

 given by fifty-seven experiments with this machine is 426.7 kilo- 

 gramme-meters. 



Puschl has investigated the fact, observed by Schmulewitsch, that 

 caoutchouc when free dilates by heating, but that when stretched it 

 contracts. From the theoretical consideration that the elasticity 

 of a body increases with the temperature when at a maximum of 

 density, and decreases when the density is a minimum, the author 

 concludes that caoutchouc has a minimum density, the temperature 

 of which diminishes as the tension increases. This temperature is 

 above the ordinary temperature for caoutchouc without tension, the 

 coefficient of dilatation being positive ; it is inferior to the ordinary 

 temperature for strongly stretched caoutchouc, the coeflicient being 

 negative. 



Violle has experimentally investigated anew the question of the 

 sun's temperature. He used a thermometer, carefully made, reading 

 to one fifth of one degree, and blackened, placed within a copper 

 sphere, also blackened. A second sphere of copjDer, externally pol- 

 ished, surrounds the first, the space between them being so arranged 

 as to have a constant current of water of any desired temperature 

 conveyed through it. On opposite sides of these concentric spheres 

 are tubulures by wdiicli the solar radiation enters, closed by a plate 

 having several openings of different sizes. His results, when re- 

 duced, show that every square centimeter of the earth's surface at 

 the places named receives the number of units of heat (gramme-de- 

 grees Centigrade) placed opposite : 



Summit of Mont Blanc 2.392 



Grands Mulets 2.262 



Glacier des Bossons 2.022 



At the level of Paris 1.745 



Assuming the correctness of Dulong and Petit's law, calculation 

 from these numbers gives 1500"^ Centigrade as the temperature of the 

 sun. But not desiring to assume this, Violle made direct experi- 

 ments with his apparatus upon the heat radiated from Siemens-Mar- 

 tin steel when running into the moulds. From the data obtained 

 he gives 1300 Centigrade as the temperature of the metal. This 

 increases only a little the previous value ; and after making all the 

 allowances fairly demanded, the author maintains stoutly that the 

 mean temperature of the sun does not sensibly difler from 2500 

 Centigrade. 



Jannetaz has studied the propagation of heat in crystallized bodies 

 in an ingenious manner. Instead of perforating the crystal plate, as 

 has been done by previous experimenters, he used a small truncated 



