iQ2 CONTINUITY. 



near neighbour, as the magnitude of such a phenomenon must 

 be inverse to its distance. I forbear to add any speculations 

 as to the cause of this most singular phenomenon. However 

 imperfect the knowledge given us by these observations, it is 

 a great triumph to have caught this fleeting object, and ob- 

 tained permanent records for the use of future observers. 



It would seem as if the phenomenon of gradual change 

 obtained towards the remotest objects with which we are at 

 present acquainted, and that the farther we penetrate into space 

 the more unlike to those we are acquainted with become the 

 objects of our examination sun, planets, meteorites, earth, 

 similarly though not identically constituted, stars differing from 

 each other and from our system, and nebulae more remote in 

 space and differing more in their characters and constitution. 



While we can thus to some extent investigate the physical 

 constitution of the most remote visible substances, may we not 

 hope that some farther insight as to the constitution of the 

 nearest, viz. our own satellite, may be given us by this class 

 of researches ? The question whether the moon possesses any 

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

 it must be exceedingly small in quantity and highly attenu- 

 ated. Calculations, made from occultations of stars, on the 

 apparent differences of the semi-diameter of the bright and 

 dark moon, give an amount of difference which might indicate 

 a minute atmosphere, but which Mr. Airy attributes to 

 irradiation. 



Supposing the moon to be constituted of similar materials 

 to the 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 which we see must be me- 

 tallic, or nearly so. The appearance of her craters is not 

 unlike that seen on the surface of some metals, such as bis- 

 muth, or, according to Professor Phillips, silver, when cooling 

 from fusion, and just previous to solidifying ; and it might be 

 a fair subject of enquiry 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 congealed 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 lunar 



