THE SOURCE OE HEAT IH THE SUN. 
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(of square miles), taking in all tlie irregularities of its form; 
and the black space, or " nucleus,' in the middle of one very 
nearly round one would kave allowed the Earth to drop through, 
leaving a thousand miles clear of contact on every side, 
and many instances of much larger spots than these are 
on record." 
Fig. 2. Fig. 3. 
The cyclones — the whirling storms of our Indian seas, 
spreading in their path death and desolation, involving alike 
fluid and solid matters in the vorticose motions — are but 
miniature representations of those mighty tornadoes of the 
Sun. It cannot, however, but be admitted that our great 
revolving storms do in many respects resemble the phenomena 
of the formation of the solar spots ; and probably, if we could 
look down upon our atmosphere as we look down upon the 
photosphere of the sun, we should discover that they had 
characters much in common. Amongst other things, our 
great cyclones and tornadoes are limited to a certain zone 
of the Earth's surface ; and the dark spots on the Sun are 
mainly confined to a zone extending to 30° or 35° in latitude 
on either side of his equator. We know not of any order 
of periodicity observed by our terrestrial storms, but obser- 
vations extending over more than half a century inform us 
that there is a regular order of increase and decrease in the 
number of solar spots. In advancing from their minimum to 
their maximum, and in again descending to their minimum, 
about — but somewhat less than — twelve years are expended, 
there being nine complete periods in a century. We have 
described the photosphere, and attempted to give an idea of 
its luminous waves. More difficult is it to convey an idea 
of the breaking up of the lines of light, the crests of the 
billows, into points, as indicating — may it be called — a boiling 
from below, and the gathering together of these black dots 
to open out into a gigantic black space, through which we 
penetrate the sphere of light, and see into the sphere of shadow 
