April 25, 1872] 



NATURE 



507 



developed by a metallic radiator of a low temperature, to 

 be enabled to demonstrate the correctness or fallacy of 

 Dulon_ij's formula. Numerous experiments have been 

 made for this purpose with apparatus of different forms, 

 the results having proved substantially alike. The device 

 most readily described consists of a spherical vessel 

 charged with water, suspended within an exhausted 

 spherical enclosure kept at a constant temperature. Re- 

 peated trials show that, when the differential tempera- 

 ture is 65", the enclosure being maintained at 60'', while 

 the sphere is 125', the dynamic energy transmitted to the 

 enclosure by a sphere the convex area of which is one 

 square foot, amounts to 5'22 thermal units per minute. 

 The accuracy of this determination is confirmed by the 

 fact that during the summer solstice at noon, when the 

 sun's differential radiant intensity is 65°, the solar calori- 

 meter indicates a dynamic energy of 5'i2 units per minute 

 on one squire foot of surface. 



Our practical investigations, then, show that a differen- 

 tial temperature of 3,000° developes by radiation a dynamic 

 energy of 1,013 thermal units per minute upon an area of 



one square foot ; and that a differential temperature of 

 65° develops S 22 units per minute upon an equal area. 

 The ratio of radiant energy at the first mentioned inten- 



•„ , r io'3 • r 1 



sity will therefore amount to . =0'337 units for each 



degree of differential temperature ; while for the low in- 



tensity it will be 



5-22 

 65 



=: o'oSo unit for each degree of 



differential temperature. Consequently, the ratio o the 



radiating energy will be 



o'337 



= 4'2( times greater at 



3,ooo° than at 65°. Now, M. Vicaire, on the autliorily of 

 Dulong, states that the ratio will be a hundred fold 

 greater for an increase of only 600°. According to Ne^v- 

 ton's theory, based on dynamic laws, the proportioa 

 betiveen the differential temperature and the radiant 

 energy of bodies is constant ; while Dulong and Petit, 

 basing their conclusions upon an erroneous estimate of 

 the time of cooling, assert that the ratio of energy increases 





several thousand times when the temperature is increased 

 from 65° to 3,000'. Newton, then, as our experiments 

 prove, is incomparably nearer the truth than the French 

 experimenters ; and possibly future research will prove 

 that^his law, when properly applied, will be found abso- 

 lutely correct. It should be mentioned that the result of 

 our experiments with the fused metal, compared with the 

 result of other experiments with solid metals at various 

 temperatures, show that the emissive power of cast iron 

 is relatively greater in a state of fusion than when solid, 

 or merely incandescent. This observed increase of emis- 

 sive power, now being thoroughly investigated, will no 

 doubt account for the deviation from the Newtonian law 

 indicated by the preceding comparison, which, let us 

 recollect, is based upon the difference of radiant energy 

 bf fused metal at 3,000', and solid metal at 65°. Con- 

 sidering this extreme range of temperature, and the totally 

 different conditions of the radiators, the observed discre- 

 pancy is not too great to admit of satisfactory explanation. 

 ' The fallacy of Dulong's formula relating to high tem- 



peratures having been conclusively shown, it will not be 

 necessary to examine the calculations of Messrs. M. E. 

 Vicaire and Sainte-Claire Deville, presented to the 

 Academy of Sciences at Paris. Besides, the question of 

 solar temperature cannot be properly investigated without 

 considering the leading points connected witli the propa- 

 gation of radiant heat through space— a subject of too 

 wide a range to be discussed in this article. It should, 

 however, be mentioned that the result of the measure- 

 ment of solar intensity March 7, 1S72, before referred to, 

 proves the correctness of our previous demonstrations, 

 showing that the temperature of the surface of the sun is 

 at least 4,036,000 F. J. ERICSSON 



THE CYCLONE IN THE WEST INDIES 



A CORRESPONDENT in your number of October 

 12, 1 87 1, expresses a wish for an article to appear 

 in your paper, on the Cyclone which passed over Antigua, 

 and several other of the Leeward Islands in the \Vest 



