On the Diminution of Direct Solar Heat in the Atmosphere, 261 



accordance with the general laws of induction, is proportional to 

 the intensity of the principal current. The excess of heat ob- 

 tained by this kind of induction is proportional to the square of 

 the intensity of the principal current. On the other hand, the 

 square of the intensity of the principal current is proportional to 

 the mechanical force used in surmounting the resistance which 

 the inducing and induced currents exert on being approached to 

 or removed away from each other. Hence it follows that, when 

 induced currents are produced by approaching or separating the 

 induced and the inducing circuit, heat is produced by induc- 

 tion. In this case the production of heat is proportional to the 

 mechanical force exerted in approaching the two circuits or in sepa- 

 rating them. 



The author has proved by a mathematical deduction, which 

 cannot be reproduced here, that the variation in the disengage- 

 ment of heat of the principal current arises from induction-cur- 

 rents of a higher order which are produced by the primary 

 current. 



XLI. On the Diminution of Direct Solar Heat in the Upper 

 Regions of the Atmosphere. By J. M.Wilson, M.A., F.G.S., 

 Fellow of St. John's College, Cambridge, and Mathematical and 

 Natural Science Master of Rugby School. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN the March Number of the Philosophical Magazine Pro- 

 fessor Tyndall has drawn attention to a note of mine in the 

 previous Number, on an observation of Mr. Glaisher's respect- 

 ing the readings of the shaded and exposed thermometers at 

 great heights. 



Professor Tyndall restates my conclusions, and, not admitting 

 them, however fairly drawn, to be representative of natural facts, 

 suggests a possible source of error in the observations arising 

 from a supposed small capacity of the black-bulb thermometer 

 for absorbing the invisible solar rays. I will not occupy your 

 space by quoting Professor Tyndall's statement, but referring to 

 it would remark that, even granting any amount of transparency 

 to the invisible rays on the part of the black bulb, the pheno- 

 menon noticed by Mr. Glaisher cannot be thus accounted for, 

 as far as I see at present, without adopting my conclusions 

 which Professor Tyndall quotes. He is doubtless right in say- 

 ing that the indications of the black-bulb thermometer are more 



Phil. Mag. S. 4. Vol. 31. No. 209. April 1866. T 



