206 M. Arago on Graham or Julia Island. 



Inclination of the most rapid slope of scoriae in the 

 same mountain. ....... 37° 



The slope according to which very fine dry sand, 

 and powdered sandstone, arranges itself, in relation to 

 the horizon, according to M. Rondelet, is an angle of 34°i 



The angle of the natural slope of common earth dry 

 and powdered according to the same architect, is . 46°| 



After moistening the earth, he found, as the mean of 

 diiferent experiments, that the angle amounted to . 50° 



We now proceed to the second class of considerations which 

 M. Arago developes. 



The island of Julia became visible between the 28th of June 

 and the 8th of July 1831 ; all doubt is confined within these 

 limits. In fact, at the former of these dates. Captain Swinburne 

 of the English service, traversed the space comprehended be- 

 tween Sciacca on the coast of Sicily, and the island Pantelaria, in 

 which the new islet has since risen, and that without observing any 

 thing extraordinary ; on the 8th July again, the Neapolitan cap- 

 tain Jean Corrao witnessed the manifest traces of the irruption. 



M. Prevost, during his voyage, obtained some information 

 which is most important as it respects the formation of the islet ; 

 for Prince Pignatelli assured him, that during the first days of 

 its appearance, as, for instance, on the 10th or 11th of July, the 

 column which ascended from the centre of the island, burned 

 during the night with a very vivid and continuous light ; the 

 Prince compared the phenomenon to theappearanceof fire-works. 



Even at the beginning of August this same column of dust 

 still gave out light, which, if not altogether so strong as the 

 Prince remarked, was at least very visible. Captain Irton and 

 Dr Davy are both vouchers of this fact. On the 5th of Au- 

 gust it is true, that Dr Davy being at some distance from the 

 island, in a situation where the impalpable powder carried along 

 by the wind fell in abundance, observed that it was not hot as 

 he received it on his hand ; but here we are not to forget the 

 amazing rapidity with which bodies that are very thin and slen- 

 der, such as burning metallic wires, for example, assume the 

 temperature of the air. With this fact in our minds, we shall 

 not be disposed to deduce from the remark of Dr Davy the con- 

 sequence that all the earthy dejections of the crater, and those 



