lia PHILOSOPHICAL TRANSACTIONS. [aNNO 1736. 



ments, if the finger of the other hand be brought near it, it will fly from the 

 finger, or be repelled by it with great vigour. 



Some Thoughts on the Sun and Moon, when near the Horizon, appearing larger 

 than when near the Zenith. By James Logan, Esq. N" 444, p. 404. 



It may perhaps be needless now to add any thing in confirmation of Dr. 

 Wallis's solution, in the Transactions, N° 187, of the sun and moon's appear- 

 ing so much larger at rising or setting, than when in a greater altitude; though 

 some have very absurdly still gone on to account for it from vapours. It is true 

 indeed, that it is these vapours, or the atmosphere alone, that make those 

 bodies, when very near the horizon, appear in a spheroidal form, by refracting, 

 and thereby raising the lower limb more than the upper; yet these can be no 

 cause of the other. The sun and moon, each subtending about half a degree, 

 appear in the meridian of the breadth of 8 or 10 inches, to some eyes more, 

 and to others less ; and in the horizon to be 2 or 3 feet, more or less, according 

 to the extent of ground they are seen over; but if one can have an opportunity 

 of seeing the sun rise or set over a small eminence, at the distance of a mile 

 or two, with tall trees on it standing pretty close, as is usual in woods without 

 underwood, his body will then appear to be 10 or 12 feet in breadth, according 

 to the distance and circumstances of the trees he is seen through ; and where 

 there has been some thin underwood, or a few saplings, Mr. Logan has ob- 

 served that the sun setting red, has appeared through them like a large exten- 

 sive flame, as if some house was on fire beyond them. Now the reason of 

 this is obvious, viz. that being well acquainted with trees, the ideas of the space 

 they take up are in a manner fixed; and as one of those trees subtends an angle 

 at the eye, perhaps not exceeding 2 or 3 seconds, and would scarcely be distin- 

 guishable, were it not for the strong light behind them, the sun's diameter of 

 above 30 minutes takes in several of them, and therefore will naturally be judged 

 vastly larger. Hence it is evident, that those bodies appear greater or less, 

 according to the objects interposed, or taken in by the eye on viewing them. 

 And to this only is that phenomenon to be imputed. 



Mr. Logan acknowledges that, this method of arguing is not new ; yet the 

 observations here given may probably tend, he thinks, to illustrate the case 

 beyond what had been advanced on the subject. 



