106 



PROCEEDINGS OF THE CANADIAN INSTITUTE. 



most painstaking observations are perhaps those of Crew and of Duner, which 

 have been worked out by three different formulae and give as results : — 



Eotation period at the equator days 25.53 ; 25.71 ; 25.50 



Rotation period near the poles days 37.66 ; 49.45 ; 45.98 



Bringing such periods to the measure of velocity we have the materials for a 

 table in which (p. is the latitude, v. the velocity, while v. sec. cf. is the velocity at 

 the equator corresponding to that observed at the various latitudes. 



It is evident that if the sun rotated as a solid, all the values of v. sec. ui. 

 should work out the same, that is, to 1.23 miles per second. But the table 

 shows that the region in latitude 74° 8^ rotates one-third less swiftly than it would 

 on that supposition. Something analogous is found in connection with Jupiter's 

 rotation, for his cloud-belts differ in their rate of movement, though not nearly in the 

 same pi-oportion. 



The consequences of this discovery have not all been reasoned out, and, as 

 Crew does not completely agrf e with Duner, further observations are necessary, 

 but the view that the gases at the visible surface of the sun are extremely tenuous 

 is much strengthened. A rt)tation of a solid sun in sections is unthinkable ; there 

 can be- nothing approaching to solidity where there are such varying rotatory 

 rates. Yet at a depth not far below the surface there must be density enough to 

 make the great gas-ball more coherent, and as the density increases the substance 

 must tend more and more to act as a viscous if not as a solid body. The sun 

 therefore appears to rotate more slowly in depth than at the surface. Again, since 

 the more rapid the rate of rotation the greater the centrifugal force, the convection- 

 currents from within the sun must be directed towards his equatorial belt, they 

 must acquire additional force in proportion as they are so deflected, which is not 

 an improbable reason for the excess of solar energy manifested near his equator. 



To treat of the Corona which envelops the sun, and has up to the present 

 time only been seen during total eclipses, would be foreign to the purpose of this 

 paper. It may, however, be remarked that attempts have been made to determine 

 whether it rotates too, and at what rate. I have only heard of one successful 

 observation, made by Deslandres in 1900, who thought it rotated faster than the 

 sun, so far at least as its west side was concerned. 



Already, however, we can picture to ourselves the sun as a star surrounded 

 by a nebula of which the greatest extension is about its equator and revolves witli 

 something like planetary velocity. It does indeed seem that the materials of 

 which the solar system is composed have not yet been completely absorbed into 

 the suQ and his planets, but that a remanet still girdles him and is seen in the 

 Corona and especially in the zodiacal light. 



What is it then that causes so sharp a distinction between the visible disc of 

 the sun and the nebula outside it ? Se.en through powerful telescopes it is as 

 definite as it appears to the unaided vision, it does not shade off by degrees like 

 comets' tails or nebular wisps. I have thought that the cold of space prescribed 

 the limit, that there is a line beyond which solar vapours cannot incandesce, like 

 that which limits the height of clouds upon the earth, alluded to at the outset. 

 Therefore, as I do not learn that any variability has been observed in the sun's 

 diameter, I have not been an enthusiastic supporter of those who think the sun's 



