66 On the Phcenomena of the Horizontal Moon. 



erroneous or nniiiiportant :" in consequence of which I 

 turned to the first voUnne, hoping to find some new hypo- 

 thesis advanced bv the doctor in his lecture upon this sub- 

 ject ; but I was disappointed. 



The doctor says, vol. i. p. 431, that " the sun, moon, 

 and stars, are much less luminous when they arc near the 

 horizon than when t!ie\' are more elevated, on account of 

 the greater quantity of their light that is intercepted in its 

 lon;rer passage through the atmosphere; we also observe a 

 much greater variety of nearer objects almost in the same 

 direction : we cannot, therefore, help imagining them to be 

 more distant when ihev ri^e or set than at any other times; 

 and, since they subtend the same angle, they appear to be 

 actually larger. For similar reasons, the apparent figure of 

 the starry heavens, even v/hen free from clouds, is that of 

 a flrittvued vault, its summit appearing to be much nearer 

 to us than its horizontal part?, and any of the constellations 

 seems to be considerably larger when it is near the horizon 

 than.whcn in the zenith." 



This explanation seems to be derived from the hypotheses 

 of Des Cartes and Berkeley; but the reader shall judge for 

 himself. 



*' Des Cartes*, and from him Dr. Wallis and most other 

 authors, account for the appearance of a different distance 

 under the same angle, from the long series of objects inter- 

 posed between the eye and the extremity of the sensible ho- 

 rizon ; which makes us imagine it more remote than when 

 in the meridian, where the eye sees nothing in the way be- 

 tween the object and itself. This idea of a greater distance 

 makes us imagine the hmiinary the larger; for an object 

 being seen under any certain angle, and believed at the same 

 time verv remote, we naturally judge it must be very large to 

 appear under such an angle at such a distance." — Hulton's 

 Mathematical Diet. vc;l. ii. p. 74. 



Mr. M(?lyneux says (Philos. Trans. Abr. vol. i. p. 221), 

 *' that if the hypothesis of Des Cartes be true, we may at 

 any time ineicase the apparent magnitude of the moon even 



* Des Ciirtes was born in 1596. 



