3j6 Mr. Lee on the dispersive power 
The dispersive power of the atmosphere will also show 
why Aldebaran and the red stars are sometimes seen projected 
on the moon’s disk in occultations by that planet, especially 
when the immersion or emersion happens to be near her 
upper limb. For the light of the moon being white, is more 
refracted than that of the star, and consequently her limb 
more elevated, which would occasion the star to appear 
within her disk a few seconds before or after contact.'f* 
The great disagreement which is found to exist in the 
declination of several of the fixed stars, as given by different 
observers, may probably be traced to the same cause, stars 
being more or less refracted according to the predominant 
colour of which their light is composed. 
That the fixed stars differ from each other in respect to the 
composition of their light, must be obvious to any one who 
will only take the trouble of comparing them on a fine night. 
They present a striking variety of colour even to the naked 
eye. But this difference becomes still more perceptible when 
they are viewed through a prism properly adapted to the eye- 
piece of a reflecting telescope. 
A star viewed in this manner is converted into a prismatic 
spectrum. Sirius and the brilliant white stars exhibit a large 
brush of beautiful violet, and the most refrangible colours in 
great abundance. Aldebaran, a Orionis, and the red stars 
show only a small proportion of those colours, whilst the 
dull white stars exhibit a great quantity of intense green 
light. 
f Vide Philosophical Transactions, Vol. LXXXIV. p. 345. Histoire Celeste 
Frangoise, Tome I. p. 393, 403, 413, 425, 428, 467, and Connoissance des Temps 
for 1817. 
