THE 



LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XXIII. FOURTH SERIES. 



LXX. An Account of Observations on Sola?* Radiation. 

 By John James Waterston, Esq* 



[With a Plate.] 



§ 1. TN March of last year I submitted to the Society some 

 -*- computations with reference to the sun's heat, and 

 suggesting a mode of deducing the potential temperature of its 

 radiating surface. This last summer I have endeavoured to put 

 this method to the proof by a series of observations on solar 

 radiation, supplemented with experiments on the rate of cooling 

 of thermometers in air and in vacuo with different kinds of radia- 

 ting surfaces, — also by another series, applying the method of 

 deducing the potential temperature of a radiating surface to pre- 

 dicate the temperature of oae that is maintained at a constant 

 known temperature. 



The success of these last mentioned, so far as they have as 

 yet been carried, encourages me to lay before the Society the 

 observations on solar radiation, with an account of the method 

 employed to obtain the results, and of the mode of reducing 

 them to a vacuum. 



§ 2. It will be remarked, on inspecting the Chart in which 

 the observations are projected f, that a simple law of atmospheric- 

 absorption is indicated, which, if confirmed by other similar 

 observations in different climates, would perhaps lead to more 

 exact ideas of the influence of the atmosphere on the sun's rays. 

 Unfortunately the best part of the summer had passed before I 

 could begin to observe, and there was almost constant interrup- 

 tion with clouds and unsettled weather. In a tropical station, 



* From the Monthly Notices of the Royal Astronomical Society with 

 Notes ; communicated hy the Author. 



t This chart is omitted, and another substituted (fig. 3, Plate V.), show- 

 ing the observations of August 21, also of August 6 and July 28, projected 

 in the same way to a larger scale. Each observation is represented by a 

 point, the coordinates of which are the reciprocal of the radiation and secant 

 of apparent zenith distance of the sun's centre. 



Phil. Mag. S. 4. No. 157. SuppL Vol. 23. 2 L 



