INDUSTRIAL PROGRESS DURING THE YEAR 1875. l v ii 



first, that silicon in combining with manganese evolves con- 

 siderable heat, and hence that the compound thus formed is 

 very stable a fact already proved for carbon. Second, that 

 the similarity of these two substances, carbon and silicon, 

 appears also when their action on iron is considered ; they 

 both act as if they were dissolved in the metal. 



Kundt and Warburg have obtained an interesting: result in 

 investigating the specific heat of mercury vapor. On the 

 kinetic molecular theory of Clausius, the quotient of the spe- 

 cific heat of a gas at constant pressure, divided by the specific 

 heat of the same gas at constant volume, should be 1.67, 

 while; in fact, for most gases this quotient is only 1.405. 

 Clausius explains this by the fact that molecules are not 

 material points, but are composed of atoms ; and only in a 

 monatomic gas would there be a correspondence with theory. 

 The molecule of mercury is shown by its vapor density to be 

 monatomic ; and it is now found by experiment that in the 

 case of this vapor the above quotient is actually 1.67. Hence 

 a molecule of mercury, so far as its theoretical and mechan- 

 ical properties are concerned, acts like a material point. 



Desains has continued his researches upon solar radiation, 

 and has determined the quantity of heat received per minute 

 at Paris by one square centimeter of the earth's surface 

 placed normal to the direction of the rays during an entire 

 year. The maximum was on June 22, when the amount re- 

 ceived was 1.29 units, and the minimum on January 30, the 

 amount being one unit. He finds also that the proportion 

 of the solar rays transmitted by a layer of water eight mil- 

 limeters thick reached its maximum on July 4, being 0.71, 

 and its minimum on April 25, being 0.63. 



Mayer has proposed a simple mode of obtaining thermo- 

 graphs of the isothermals of the solar disk by the use of 

 Meusel's double iodide. Thin paper, smoked on one side, is 

 covered on the other with the iodide, and is exposed to the 

 sun's image, formed by a telescopic object-glass, the aperture 

 being at first only that necessary to give the smallest area 

 of blackened iodide with a sharp contour. This he calls the 

 area of maximum temperature. On enlarging the aperture, 

 the black area gradually extends, forming a series of new 

 isothermal lines with the successive enlargements. Some in- 

 teresting conclusions have already been reached, and it is 



