THE MOON. 



1. ESTIMATED merely by its magnitude, the moon is among the 

 most inconsiderable of the bodies which compose the Solar 

 System. It has not, as will presently appear, even that interest 

 which must attach to a globe adapted for the habitation of 

 organised races, analogous to those for whose dwelling the earth 

 has been appropriated. Nevertheless it has ever been regarded by 

 mankind with sentiments of profound and peculiar interest, and 

 has been invested by the popular mind with various influences, 

 affecting not only the physical condition of the globe, but also 

 directly connected with the organised world. It has therefore 

 been as much an object of popular superstition as of scientific 

 observation. These circumstances are doubtless owing in some 

 degree to its striking appearance in the firmament, to the various 

 and rapid succession of changes of apparent form to which it is 

 subject, and above all to its proximity to, and close alliance with 

 our planet. We propose on the present occasion to give a general 

 account of its motion, magnitude, and physical condition ; and 

 to explain more particularly those circumstances which lead to 

 the conclusion that, unlike the planets, the moon presents none of 

 the analogies to the earth which would render it at all probable or 

 even possible that it can be a habitable world. 



2. It has been ascertained, that its distance is very little less 

 than 240000 miles ; and since the semidiameter of the earth is 

 4000 miles, it follows that the moon's distance is about sixty 

 semidiameters of the earth. The method of ascertaining this dis- 

 tance differs in nothing that is essential, from that by which a 

 common surveyor ascertains the distance of an object on the earth 

 which is inaccessible to him. 



3. Now the least reflection will render it apparent that the 

 moon must move round the earth, in a path which cannot differ 

 much from a circle of which the earth is the centre. This 

 follows from the fact with which every one is familiar, that its 

 apparent magnitude is always nearly the same. It is, therefore, 

 always at the same or nearly the same distance from the observer. 

 The earth must consequently be placed in the centre of its path, 

 and that path must be nearly a circle. 



4. When the distance of a visible object is determined, its 

 magnitude may easily be ascertained by comparing it with any 

 other object of known magnitude at a known distance. Let us 

 take, for example, a halfpenny, which measures about an inch 

 in diameter, and let it be placed between the eye and the moon. 

 It will be found on the first trial that the coin will appear larger 

 than the moon ; it will, in fact, completely conceal the moon from 

 the eye, and produce what may be termed a total eclipse of that 

 luminary. Let the coin be moved however further from the eye, 



