120 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



experimentally proved by J. W. Draper, and it would be a re- 

 sult of great importance to determine the law of growth of 

 refrangibility with temperature. If this could be achieved, 

 a very convenient and accurate pyrometer could be made of 

 the ordinary spectroscope. An accurate investigation of 

 this subject has been undertaken by a committee of the Brit- 

 ish Association, which has in a preliminary report presented 

 some observations on the simple increase of radiation with 

 temperature. On this subject Becquerel has a great number 

 of observations, whence he infers that the differences between 

 the logarithms of the luminous intensities are proportional to 

 the differences of temperature, a law which he thinks would 

 hold up to 1200 degrees Centigrade; but the law as thus 

 expressed mathematically by no means represents the true 

 rate of increase of the total luminous intensity, which is, in- 

 deed, very much slower than that required by Becquerel's 

 law. Again, if the law of Dulong and Petit for the velocity 

 of cooling be true, then the amount of heat radiated, as also 

 the temperature, could be calculated ; but on comparison 

 with actual observations at high temperatures it is found 

 that their law gives too rapid an increase for the total radi- 

 ation. Assuming, however, these laws to be even approxi- 

 mately correct, we may calculate the hypothetical tempera- 

 ture corresponding to the brightness and total radiation 

 from the sun, and deduce in one case for the solar tempera- 

 ture 13,000, and in the other case 11,000 degrees Centigrade. 

 Report of the British Association, 1873, 40 1. 



THE DIFFUSION BETWEEN DRY AND MOIST AIR. 



An investigation that may have some interest in the fut- 

 ure of meteorology has been conducted by Dufour, who has 

 examined the question of the diffusion between dry and moist 

 air traversing a porous disk. He finds that the activity of 

 the diffusion does not depend directly, except possibly in a 

 very slight degree, upon temperature. If we compare the 

 observations made at different temperatures, we find that the 

 activity of the diffusion also does not depend, with slight ex- 

 ception, upon the relative humidity; it depends principally 

 upon the difference between the quantities of vapor, or the 

 tensions of the vapor, on the opposite sides of the disk, and 

 is in fact very nearly proportional to the difference of the ten- 



