The Horizontal Moon. 



By Rkv. J. T. Pettek. 



As known to every one the moon appears much larger on the 

 horizon than on the meridian, though it is then four thousand 

 miles farther from us; by instrumental measurement it is smaller, 

 but to the naked eye larger. Why is this? Some have supposed 

 that the denser atmosphere near the earth operates as a lens, and 

 actually magnifies; but if this were so the amplification would ap- 

 pear in the telescope, as well as to the naked eye, and the instru- 

 mental measurements would be larger instead of smaller. What 

 then is the reason ? 



This question used lo be a good deal discussed by pliilosophers. 

 Gassendus, Descartes and Hobbes all tried their hand at it; and 

 one hundred and sixty years ago Bishop Berkely labored on it 

 through fourteen pages of his Minute Philosopher. About 1660 

 the learned Dr. Wallis contributed an article to the British Philo- 

 sophical Transactions, in which he explained the phenomena in 

 this way : 



We see the rising moon beyond all objects along the line of 

 sight, and therefore think it farther off than it really is, and this 

 illusion makes it appear larger. And this explanation (for the 

 want of a better; has been accepted by astronomers. I doubt 

 whether any astronomer was ever really satisfied with it. I am 

 sure the ordinary observer is not. It implies a comparison whicii 

 we never make when looking at the rising moon, and which the 

 little child, or unlettered peasant, to whom it appears as much 

 larger than the meridional moon as it does to us, is utterly unable 

 to make. And then, as justly observed by Bishop Berkely, if we 

 saw it from behind a wall which cut off all intervening objects, it 

 would appear no larger than on the meridian ; or, as we may ob- 

 serve, if looked at tluough a tube, or seen rising over the sea, or 

 above a prairie. 



