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LXXII. An Attempt to affign the Caufe y why 
the Sun a?id Moon appear to the naked Eye 
larger when they are near the Horizon . 
With a?i Account of fever al natural Phe- 
nomena) relative to this SubjeSl . By Mr . 
Samuel Dunn. 
Chelfea, January 27, 1762. 
Read Feb. n, j, t u Sun and Moon, when they 
l?62, are in or hear the horizon, ap- 
pear to the naked eye of the generality of perfons, fo 
very large in comparifon with their apparent magni- 
tudes, when they are in the zenith, or fomewhat ele- 
vated, that feveral learned men have been led to en- 
quire into the caufe of this phenomenon, and, after 
endeavouring to find certain reafons, founded on the 
principles of phyfics, they have at lafi: pronounced 
this phenomenon as a mere optical illufion. 
2. The principal difiertations, which I have- hi- 
therto feen, conducing to give any information on 
this fubjedt, or helping to throw any light on the 
fame, have been thofe printed in the Tranfadtions of 
the Royal Society, the Academy of Sciences at Paris, 
the German Adts, and Dr. Smith’s Optics ; but as all 
the accounts, which I have met with in thefe writings, 
any way relative to this fubjedt, have not given me 
that fatisfadtion which I have defired, curiofity has 
induced me to enquire after the caule of this lingular 
phenomenon, in a manner fomewhat different from 
that which others have done before me, and by fuch 
2 experiments 
