240 J. R. Mayer on Celestial Dynamics. 
enlargement of his apparent diameter to the extent of one second, 
the smallest appreciable magnitude, would require from 33,000 
to 66,000 years. 
Not quite so unappreciable would be the increase of the mass of 
the sun. If this mass, or the weight of the sun, were augmented, 
be the consequence, whereby their times of revolution round the 
central body would be shortened. The mass of the sun is 271 
quintillions of kilograms; and the mass of cosmical matter an- 
nually arriving at the sun stands to the above as 1 to from 21 to 
42 millions. Such an augmentation to the weight of the sun 
ought to shorten the sidereal year from gaamth to sasmnth of its 
length, or from $ths to 8ths of a second. , 
e observations of astronomers do not agree with this con- 
clusion; we must therefore fall back on the theory mentioned at 
the beginning of this chapter, which assumes that the sun, like 
the ocean, is constantly losing and receiving equal quantities © 
matter. This harmonizes with the supposition that the vis viva 
of the universe is a constant quantity. 
VIL. The Spots on the Sun's Disc. 
The solar disk presents, according to Sir John Herschel, the 
following appearance. ‘‘ When the sun is observed through @ 
owerful telescope provided with colored glasses in order to 
essen the heat ats : 
eyes, large dark spots are often seen surrounded by edges which 
ich are 
before. When they disappear, the darker part in the middle of 
the spot contracts to a point and vanishes sooner than the edges, 
ate 
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