146 Royal Astronomical Society. 



having modern volcanoes following the direction of the higher edges 

 of their chains. Professor Ponzi seems to think it unquestionable 

 that water existed at the surface of the moon ; the fierce glare of the 

 sunshine is not able to melt the ice there, which is probably at the 

 temperature of the planetary spaces ; just as the sun at the surface 

 of the earth is not able to melt our glaciers, which yet possess a cer- 

 tainly higher temperature. Cold, and other unknown causes, may 

 have absorbed and fixed all the atmosphere which anciently existed, 

 as we see that the immense atmosphere which anciently surrounded 

 the earth has been fixed by several chemical processes and reduced to 

 its actual composition ; and it might be possible that this actually 

 existing atmosphere of ours should be all solidified, either by cold or 

 chemical processes, if the earth arrives at the same degree of cold 

 which seems to have place on the moon. 



*' These are some of the conclusions to which we have arrived in 

 our inquiry into the solar and lunar constitution ; they do not cer- 

 tainly belong to astronomy strictly taken, but a recreation from 

 more serious occupations may be excused to astronomers dwelling 

 in the pure climate of Italy. I trust you will receive them as a 

 token of my gratitude, and of interest for the work whicli you have 

 published." 



In a later letter Professor Secchi tells Captain Manners "that 

 the observatory of the CoUegio Romano is about to be furnished 

 with a large refractor equatoreally mounted. The refractor will 

 have 9 inches aperture, and a focal length of 14 French feet." 

 There is only a little hesitation at present as to the best mode of 

 mounting this telescope. 



Since the date of the preceding communication, Sig. Secchi has 

 made the following interesting experiments on the heat emitted by 

 different parts of the solar disc. It appeared from the former experi- 

 ments that the heat increased from the margin of the solar disc to 

 the centre ; but there was this peculiarity, that when it was mea- 

 sured in the direction of the axis of the sun's rotation, it attained 

 its maximum intensity at a point situate about 3' above the centre. 

 At the time when the former experiments were made, the projection 

 of the sun's equator upon his disc passed above his centre, at a di- 

 stance agreeing almost exactly with the position of maximum tem- 

 perature ; whence the conclusion naturally suggested itself to Sig. 

 Secchi, that the equatoreal regions of the sun are intrinsically hotter 

 than the other parts of his surface. He justly remarked, that if this 

 were true, it ought to follow that in the month of June, when the 

 nodes of the solar equator pass through the earth, the upper and 

 lower hemispheres should appear equally heated ; and on the other 

 hand, in the month of September, when the projection of the solar 

 equator attained its greatest dej)ression, the point of maximum 

 temperature should fall below the centre of the disc. Experiments 

 similar to those previously undertaken by him have served to con- 

 firm this view of the subject. " In the month of August the upper 

 hemisphere appeared a little hotter than the lower, but the differences. 



