368 ANNUAL OF SCIENTIFIC DISCOVERY. 



during which I have been able to try the experiment. In the autumn 

 of 1851, after my return from observing the total solar eclipse in 

 Sweden, it occurred to me that the best chance of obtaining a sight 

 of these phenomena might be afforded by taking advantage of that 

 state of sky, lovely indeed, but too rarely seen in this country, when 

 detached and sharply defined clouds are slowly moving over the deep 

 blue surface of the heavens. On two or three such occasions, the 

 clock-movement of my equatorial having been carefully regulated, I 

 watched the passing of well-defined clouds over the sun, which cer- 

 tainly seemed to produce a rather darker tint of sky in the immediate 

 vicinity of the sun's edge than any artificial contrivance in the eye- 

 piece. Yet the advantage gained was not such as to give the slightest 

 hope of success. If it is at all possible to render these extremely 

 delicate phenomena visible by artificial means, it will probably be 

 accomplished by erecting a suitable instrument on the top of one of 

 the highest accessible mountains in a fine climate, like that of Oroo- 

 miah in Persia, as described by Mr. Stoddart, where the smaller den- 

 sity of the atmosphere and its great dryness exceedingly diminish its 

 illumination by the sun's rays. A telescope of very moderate size 

 might answer the purpose, if equatorially mounted and driven accu- 

 rately by clock-work. 



LUNAR VOLCANOES. 



The following observations on the nature of lunar volcanoes have 

 been made by Prof. Secchi, of Rome. 



" The first class of the lunar volcanoes possesses a distinctive char- 

 acter ; the edges of the craters are almost completely obliterated, 

 so that their border now is a continuation of the plane ground, in 

 which they seem excavated, and a deep well only remains in the place 

 of the ancient mouth of the volcano. Instances of this kind are very 

 frequent near the south pole of the moon, and around the large spot 

 Tycho ; but Tycho itself does not belong to this class. The physiog- 

 nomy of these craters nearly resembles our submarine volcanoes of 

 the Monti Ciminii, to the N. W. of Rome. The country around the 

 craters of Bracciano, Bolsena, and di Vico, is almost flat, and the old 

 openings of the craters are now deep lakes. On this ground we are 

 led to believe that even in the moon many subaqueous volcanoes ex- 

 isted. Another distinct character of these volcanoes of the first class 

 is, that they are in a line, as if they burst from the cracks of the solid 

 body of the crust produced by earlier formations ; this is most strik- 

 ing in Arzahel, Alphonsus, and many others, and they seem to follow 

 the cracks made by the soulevement which raised Tycho, the lunar 

 Apennines, &c. Some of the higher chains of lunar mountains 

 are seen visibly parallel to the allignment of the craters : this fact 

 also is like that which we observe on the earth ; indeed, the large 

 Italian volcanic chain follows the line of the Apennines along this 

 country. 



" The second class of lunar volcanoes are those which have their 



