[ 47 1 ] 
is a maximum of the apparent magnitude of the nu- 
cleus, as feen by the naked eye. 
22. Among the fixed ftars, may be obferved a Gi- 
verfity of colour and fplendour, iomevvnat like tha 
diverfity, which is obfervable among thole terreftrial 
lights. " Some fixed ftars are more fharply defined 
than others, fuch are generally white, and their vi- 
bratory fcintillations more quick and fmart. Others, 
which twinkle more flowly, are generally more red 
and large. In the zenith, they appear almoft all of 
them entirely free from twinkling; and in the hori- 
zon, they are fo invelloped in vapours, as to be un- 
difcernible ; at their firft appearance after rifing, or 
laft appearance before fetting, they twinkle more 
flow. It feems, therefore, not only probable, that 
the atmofphere is the caufe of their apparent fcintilla- 
tions ; but that, could the diftance of one fixed ftar be 
obtained, the diftances of fome others might be eflayed 
at, by analogy of their colours, and vibratory fcintil- 
lations. Poflibly alfo, we may acquire fome know- 
ledge of the nebulous ftars, from like confiderations. 
23. For the reafons which have been communi- 
cated, it has appeared to me, that the Sun and Moon, 
and diftances of ftars near the horizon, do appear en- 
larged to the naked eye; becaufe they then appear 
nearer to us. That they then appear nearer to us, 
and more faint ; becaufe then their rays pafs through 
a greater length of the atmofphere and horizontal va- 
pours. That in fo palling through a greater length of 
the atmofphere and horizontal vapours, thofe rays are 
fo reflected, refrafted, infle&ed, attracted, refifted, 
accelerated, or retarded, fo as to become more diver- 
gent than they otherwile would, at their entrance into 
Vol.LII. Ppp the 
r» 
