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'' (Hersciiel, § 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" 1 

 which have been observed, and which, when attentively watched, are found to be 

 always changing in appearance (IIerschel). 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 (Herschel's " cloudy stratum,'") would be cleared away for a certain space 

 under the central parts of the storm b} r 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 Mould cause varying streaks 

 of light. These are exactly the circumstances assumed by Sir William Hersciiel 

 to account for the great spots with their dark centres surrounded by sharply 

 terminated penumbrse inside the abrupt ragged boundaries of .the bright surface, 

 and the branching luminous streaks or " faculae" in the bright surface outside 

 in their neighbourhood. — (Sir John Herschel'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 



surface having a mass equal to ^ — 7777 = ^ °f ms own mass - This is equal to 



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 



