78 PROFESSOR W. THOMSON ON THE 
vapour, which a few miles outside revolves at the rate of 277 miles per second 
about the equatorial regions, and (if not at the same) certainly at enormously great 
rates a few miles from the Sun’s surface in other localities. Such eddies may 
ordinarily be seen as the streaks which have been compared to “ the streamers 
of our northern lights” (HERscHEL, § 387), and when any one of them sends a root 
down to the Sun’s surface it may cause one of the “‘ minute dark dots or pores” 
which have been observed, and which, when attentively watched, are found to be 
always changing in appearance (HerscHeL). A great rotatory storm, like the 
tropical hurricanes in the earth’s atmosphere, may occasionally result from 
smaller eddies accidentally combining, or from some disturbing cause origi- 
nating at once an eddy on a much larger scale than usual, and may traverse the 
Sun’s surface, preventing the distillation of meteoric vapour over a great area, and 
consequently checking both the supply of dynamical energy for radiant heat in the 
luminous atmosphere of resistance, and the torrents of condensed meteoric vapours 
falling to the surface below it. The consequence would be, that the meteoric 
rain (HerscHe.’s “ cloudy stratum,”) would be cleared away for a certain space 
under the central parts of the storm by falling down to the liquid or solid surface, 
and the luminous atmosphere would lose intensity over a larger space bounded 
very irregularly by a region of minor eddies, which would cause varying streaks 
of light. These are exactly the circumstances assumed by Sir Witt1am HERSCHEL 
to account for the great spots with their dark centres surrounded by sharply 
terminated penumbree inside the abrupt ragged boundaries of .the bright surface, 
and the branching luminous streaks or “ facule” in the bright surface outside 
in their neighbourhood.— (Sir Joun Herscuet’s Astronomy, § 388). 
No. IV. (Added August 15, 1854.) On the Age of the Sun. 
The moment of the Sun’s rotatory motion (according to the hypothesis men- 
tioned above in the “ Explanation of the Tables” regarding the moment of inertia 
of his mass) is one-third of his mass multiplied by his radius, multiplied by the 
linear velocity of his equator; and is therefore equal to that of a planet at his 
pela i el 
3x277 650 
the quantity of meteoric matter which would fall in during 25,000 years, at the 
present rate; and therefore 25,000 years is the time the Sun would take to acquire 
his actual motion of rotation, by the incorporation of meteors, if these bodies were 
each revolving in the plane of his equator immediately before entering the region 
of intense resistance. But it has been shown to be probable that a great space 
round the Sun is occupied by a vortex of evaporated meteors, and that the incor- 
poration of meteoric matter takes place in reality by the condensation of vapour 
in a stratum close to his surface all round. It appears not improbable that the 
surface having a mass equal to of his own mass. This is equal to 
