Intelligence and Miscellaneous Articles, 315 



a Millstone-Grit area ; 3, their conformity to the underlying Mill- 

 stone-Grit rocks, and the unconformity of the overlying Magnesian 

 Limestone; 4, their containing plant-remains similar to those of 

 the Millstone-Grit ; 5, their colour. Their purplish tint, and re- 

 semblance to certain German " Eothliegende " conglomerates, are 

 the only characters which seem to unite them with beds of that age. 



XL IV. Intelligence and Miscellaneous Articles. 



RESEARCHES ON SOLAR RADIATION. 

 BY MM. P. DESAINS AND E. BRANLEY. 



WE have the honour of laying before the Academy an account 

 of some experiments we have made this summer with the view 

 of solving certain questions relative to solar radiation. These ques- 

 tions are : — 



1. The influence of altitude on the intensity of the calorific action 

 exerted by the sun at points whose projections on the ground are 

 not very distant from each other. 



2. The influence of the altitude of a point on the composition of 

 the sun's rays which strike it. 



3. How the composition of the heat sent to the same point varies 

 with the height of the sun above the horizon when the quantity of 

 vapour contained in the air does not vary during the experiments. 



The apparatus we used had been previously constructed by M. 

 Duboscq and M. Ruhmkorflr under the direction of one of us (M. 

 Desains). We will give a rapid description of it. 



The first partis a parallactic apparatus consisting of a Silbermann's 

 heliostat, the clockwork of which moves not as usually a mirror, but 

 a tube whose axis follows the sun in its daily course. 



This tube has a double envelope ; and its inner chamber has a ther- 

 moelectric pile, on one face of which the sun's rays strike when a 

 stop is removed which closes the corresponding end of the tube in 

 which it is placed. In the tube itself, between the end and the 

 pile, diathermanous screens may be placed so as to act on the inci- 

 dent rays. 



The second apparatus used in our researches is more easily trans- 

 portable than that we have just described. One of its principal parts 

 is a leg with a double movement, which supports at the top a copper 

 tube about 0*06 metre in length by 0*05 metre in diameter. The 

 movements with which the apparatus is furnished render it possible 

 to keep its axis continually pointing to the centre of the sun ; and, 

 thanks to a system of lateral sights, it is always possible to judge 

 whether the condition is fulfilled. 



In this tube or moveable support a thermoelectric pile may be fixed, 

 provided with an envelope identical in all respects with that we have 

 described above. 



Instead of the pile it is sometimes advantageous to introduce 

 the blackened bulb of a thermometer, the stem of which projects 

 through an aperture constructed for that purpose. 



It is also possible to introduce a spectroscope of a particular kind, 



