VOL. XVI.] yHILOSOPHICAL TRANSACTIONS. SSQ 



And this might do something to the purpose, if we find it true in our case. 

 First then, says he, the duskiness of the moon near the horizon admits the 

 pupil to enlarge itself, the crystalline to flatten, and the eye to lengthen : but 

 what if we change our object, and instead of the moon take the distance between 

 some of the fixed stars, as suppose those of Orion's girdle ; we shall find the 

 same phenomenon in them, and yet I hope neither he nor Gassendus will assert, 

 that they at one time strain the eye more than at another, or that at any time 

 their lustre strains the eye at all. But perhaps he will then say, that this other 

 reason holds, which is, 2dly, that the greater imaginary distance, at which we 

 think the moon near the horizon than when more elevated, makes us contem- 

 plate her as if really she was so, viz. with enlarged pupils, &c. But this has 

 been sufficiently refuted in my remarks against Descartes, and if there were any 

 thing in this surmise, the horizontal moon should be fancied near to us rather 

 than farther from us. 



Riccioli, in his treatise on refraction, asserts, that he and Father Grimaldi 

 had often taken the horizontal sun and moon's diameters by a sextant, when 

 to the naked eye they appeared very large, Grimaldi directing his sight to the 

 left edge, and Riccioli to the right, and that even by the instrument they 

 always found the diameters greater than when more elevated, the sun often 

 subtending an angle of almost a degree, and frequently 45 minutes, the moon 

 also 38 or 40 minutes. Now this is directly contrary to the matter of fact, 

 which I have before alleged, and directly repugnant to the matter of fact asserted 

 by the French Abbe in the aforecited journal. Whether of us be in the right, 

 I leave to accurate experiment to determine, and submit the whole to the deci- 

 sion of the illustrious Royal Society. Only had Riccioli's experiments been ac- 

 curately prosecuted, he should have tried them when the horizontal moon had 

 looked 10 times larger in diameter than ordinary ; and then if it be true, that 

 even by an instrument she will be found proportionally broader than really, she 

 should subtend an angle of 300 minutes, or 5 degrees ; for very often I have 

 seen the moon when she appeared 10 times broader than ordinary, which the 

 small addition of 8 or 10 minutes to her usual diameter could never cause. 



The Sentiments of Dr. John fVallis, R. S. Soc. on the aforesaid Appearance. 

 Communicated in a Letter to the Editor. N° 187, P« 323. 

 As to the last inquiry, concerning which, you say, the Royal Society would 

 be glad to know my opinion about the apparent magnitude of the sun near the 

 horizon, greater than when considerably high; the inquiry is ancient, and, I 

 remember discoursing of it near 40 years ago with Mr. Foster, then professor 

 of astronomy in Gresham College, who then assured me, from his own obser- 



VOL. III. 3 B 



