Ix KEl'ORT — 18GU. 



by this class of researches ? The yiiesiiuu \vhether the inoou possesses any 

 atmosphere may still be regarded as unsolved. If there be any, it must be 

 excecdiuglj small in quantity and highly attenuated. Calculations, made 

 from occultation of stars, on the apparent differences of the scmidiameter of 

 the bright and dark moon give an amount of diiference •which might indicate 

 a minute atmosphere, but which Mr. Airy attributes to irradiation. 



Supposing the moon to be constitiited of similar materials to tlie earth, it 

 must be, to say the least, doubtful whether there is oxygen enough to oxidate 

 the metals of which she is composed ; and if not, the surface Avhich we see must 

 be metallic, or nearly so. The appearance of her craters is not unlike that 

 seen on the surface of some metals, such as bismuth, or, according to Professor 

 Phillips, silver, Avlieu cooling from fusion and just previous to solidifying ; and 

 it might be a fair subject of inquiry whether, if there be any coating of oxide 

 on the surface, it may not be so thin as not to disguise the form of the con- 

 gealed metallic masses, as they may have set in cooling from igneous fusion. 

 M. Chacornac's recent observations lead him to suppose that many of the 

 limar craters were the result of a single explosion, which raised the surface 

 as a bubble and deposited its debris around the orifice of eruption. 



The eruptions on the surface of the moon clearlj- did not take place at one 

 period only, for at many parts of the disk craters may bo seen encroaching 

 on and disfiguring more ancient craters, sometimes to the extent of three or 

 four successive displacements : two important questions might, it seems to me, 

 be solved by an attentive examination of s\ich portions of the moon. Bj' ob- 

 serving carefully with the most powerful telescopes the character of the ridges 

 thus successively formed, the successive states of the lunar surface at different 

 epochs might be elucidated ; and sccondlj-, as on the earth we should look for 

 actual volcanic action at those points where recent eruptions have taken place, 

 BO on the moon the more recently active points being ascertained h\ the suc- 

 cessive displacement of anterior formations, it is these points which should be 

 examined for existing disruptive disturbances. Metius and Fabricius might 

 be cited as points of this character, having been found by M. Chacornac to 

 present successive displacements and to be perforated by numerous channels 

 or cavities. M. Chacornac considers that the seas, as they are called, or 

 smoother portions of the lunar surface have at some time made inroads on 

 anteriorly formed craters ; if so, a large portion of the surface of the moon 

 miist have been in a fused, liquid, semiliquid, or alluvial state long after the 

 solidifying of other portions of it. It would be difficult to suppose that this 

 state was one of igneous fusion, for this could hardlj* exist over a large part 

 of the surface witliout melting up the remaining parts ; ou the other hand, 

 the total absence of any signs of water, and of any, or, if any, only the most 

 attenuated, atmosphere, would make it equally difficult to account for a largo 

 diluvial formation. 



Some substances, like mercury on this planet, might have remained liquid 

 after others had solidified ; but the problem is one which needs more exami- 

 nation and study before any positive opinion can be pronounced. 



I cannot pass from the subject of lunar physics M'ithout recording the obli- 

 gation we arc under to our late President for his most valuable observations 

 and for his exertion in organizing a band of observers devoted to the exami- 

 nation of this our nearest celestial neighbour, and to Mr. Xasmyth and Mr. 

 De la Hue for their important graphical and photographical contributions to 

 this subject. The granular character of the sun's surface observed by Mr. 

 Nasmyth in lb6U is also a discovery which ought not to be passed over in 

 silence. 



