374 



Specific Heat. 



Sand of the Experimental Garden, . . . 0.19432 



Sandstone of Craigleith Quarry, . . . 0.1925? 



Another experiment, . . . . 0.19152 



Mean, . . . 0.19205 



Some correction would no doubt require to be made for the quan- 

 tity of moisture contained in the rocks. 



4. On the Effect of Snow in apparently increasing the Force 

 of Solar Radiation. By Professor Forbes. 



Referring to a communication made by him to the Society on the 

 1st February 1841 (see Proceedings, page 322), the author re- 

 minded the Society that he had then endeavoured to account for cer- 

 tain anomalous facts observed by Dv Richardson, connected with 

 solar radiation in the Polar Regions, by adverting to the intense 

 radiating effect of a covering of snow. The disappearance of this 

 snowy covering in the month of May, the author had observed to be 

 synchronous with the anomalous diminution of solar radiation, ascer- 

 tained by a blackened thermometer, in the months of June and July, 

 compared with the months of April and May. 



Professor Forbes endeavoured to verify his conjecture, by direct 

 experiments on the force of the sun amongst the snowy mountains 

 of Switzerland ; and it was so completely borne out, that the limited 

 range of his instrument (Leslie's photometer) was in clear weather 

 always outrun, when it was exposed on a snowy surface ; and even 

 when placed upon a dark rock (on the moraine of a glacier), the I'e- 

 flected light fi'om the neighbouring snowy summits was so intense 

 as to give extraordinarily high indications. Owing to the construc- 

 tion of the instruments, he was unable to estimate their readings 

 correctly ; but he hopes to make moi'e accurate observations during 

 the ensuing summer. Sir John Herschel's actinometer gave a 

 value of the solar radiation nearly independent of its position upon 

 snow or rock. 



The following Donations were presented to the Society 

 since the last Meeting : — 



Annuaire de I'Observatoire Royal de Bruxelles. Par A. Quetelet, 

 Directeur de cet Etablissement. 1842. — Bi/ the Author, 



Nouveaux Catalogue des Principales Apparitions d'Etoiles Filantes. 

 Par A. Quetelet. — By the Author. 



I 



