5[§4 '^'-'^ ^^ "^"^ HORIZONTAL MOON. 



cipleis : After perufing thefe obje6tIons, can he blame me for 

 reje6iing his hypothefis. As for Mr. D.*s remarks on my 

 theory of mixed gafes, they require no anfwer ; becaufe he 

 profeffes not to underftand it. I am willing, however, to 

 fubmit the merits of it, as well as its claim to the title of a 

 'theory, to thofe mechanical philofophers who happen to com- 

 prehend it. 



JOHN GOUGH. 



V. 



On ilte apparent Size of the horizontal Moon, In a Letter from 

 Mr. EzEKiEL Walker. 



DEAR SIR^ 



Enlarged appear, 

 ance of the ho- 

 rizontal moon. 



Attempts to ac- 

 count for it. 



To Mr. NICHOLSON. 



HEN the full moon is juft rifing above a clear horizon, 

 (he is an object that pleafes every eye : But at the fame time 

 that (he pleafes the eye of the philofopher, fhe embarrafles his 

 reafon, to affign the caufe of her apparent magnitude's being 

 fo milch greater near the horizon, than at higher elevations. 

 ■ When men in former ages began to reafon on this phenome- 

 'non, they imagined that the angle fubtended by the moon, was 

 Yeally increafed, by arefradion of her rays, in paffing througli 

 the vapours contained in the air, near the earth's furface. But 

 when it became known that the fubtended the lead angle at the 

 eye, when her apparent magnitude was greateft, philofophers faid 

 that the eye was impofed upon by the long feries of objeds 

 interpofed between the eye and the extremity of the fenfibfe 

 horizon. And after It was difcovered that the fame pheno- 

 menon was bbferved at fea, where no land obje6ts could be 

 Teen, they blamed the clouds for deceiving them ; and when 

 the clouds fle>)v away, the fpirit of inquiry flew after them, 

 to feek for information in the apparent concavity of the Iky. 



Such were the erroneous opinions maintained by men of the 

 greateft celebrity, both in ancient and in modern times. To 

 mention any more of them would be ufelefs labour : a fingle 

 quotation from Dr. Smith's Optics will, I prefume, be quite 

 fufficient to fhow how little was known of this matter at the 

 time when he wrote. 



After 



