44^ Royal Astronomical Society, 



image, and in the last is below it. But it is not impossible that 

 the two solar hemispheres should possess different temperatures, as 

 seems to be the case on the earth, and is suspected in Mars. If 

 this is the case, these researches will throw some light on the clima- 

 tology of the earth itself; since the heat of the sun must be different, 

 according as one or the other of its poles is turned towards the 

 earth. Future experiments will resolve this question. With re- 

 spect to the poles of the sun, I shall add here a conjecture on a fact 

 recently discovered by Captain Sabine. The journal Institut re- 

 lates that this gentleman has found that the deviation of the mag- 

 net from its mean position at the Cape of Good Hope is found to be 

 in opposite directions at the epochs of the two equinoxes. Might 

 this not be an effect of the solar magnetical polarity on the terres- 

 trial magnetism ? The fact deserves to be examined, if it takes 

 place in our hemisphere, and in opposite directions. Coming again 

 to the solar heat, I have found that spots seemed less hot than the 

 rest ; but as only small groups of them were visible, no singular 

 fact or law can be stated from these observations. I shall conclude 

 this account by noticing an odd historical coincidence, namely, that 

 these observations were made in the same room where it is said F. 

 Scheiner, the first who used a telescope mounted equatorially, made 

 his observations of the sun. This room has been this year added to 

 the observatory. 



" I shall now briefly expose to you some considerations on the 

 theory of lunar formations, which have been the subject of some dis- 

 cussions with our eminent geologist. Professor Ponzi, whom I gladly 

 engaged in these researches. He is exceedingly well acquainted 

 with the terrestrial volcanoes, both ancient and modem (being now 

 occupied in the description of the Roman States), and with Italian 

 geology ; the conclusions to which we have arrived are these : — The 

 lunar volcanic formations must be distributed into three classes, to 

 which a fourth class may be added analogous to our Plutonian for- 

 mations. 



" The first class of the lunar volcanoes possesses a distinctive 

 character ; that the edges of the craters are almost completely obli- 

 terated, 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 physiognomy 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 vol- 

 canoes existed. 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 striking in Arzahel, Purbach, Alphonsus, and many others, 

 and they seem to follow the cracks made by the souUvement which 



