PROCEEDINGS OF THE CANADIAN INSTITUTE. 105 



not liquid, it must be abandoned. I have seen a large dark spot which seemed to 

 show on the western limb as an indentation, but the effect might be produced by 

 a dark mass covering a considerable surface or by the obscuration of that surface 

 otherwise, and I incline to the belief that some emission from the interior spreads 

 over the surface of the photosphere in the form of vapour, some matter which 

 iua pedes the transmission of radiations giving light and perhaps heat as their 

 effects, but does not so impede or absorb the radiations which cari-y electrical 

 charges. 



Whatever may be the cause of spots, they were seized upon as affording 

 means for determining the time of solar rotation, and Sir John Herschell, in his 

 Astronomy, edition 1842, thus summed up this branch of the subject : — 



" Our telescopes show us dark spots upon its (the sun's) surface, which slowly 

 change their places and forms, and by. attending to whose situation at dift'erent 

 times astronomers have ascertained that the sun revolves about an axis, inclined at a 

 constant angle, of 82° 40' to the plane of the ecliptic, performing one rotation in a 

 period of 25 days, and in the same direction with the diurnal rotation of the 

 earth." 



Some further elements of supposed precision having been introduced by Mr. 

 Carrington, the Greenwich Observatory adopted and keeps to a rotation period of 

 25.38 days, sidereal. 



I found, however, as a very casual observer may easily do, that this period 

 did not suit the spots I examined, with a view to discover if there were not 

 permanently active regions on the sun, answering to volcanic districts upon the 

 earth. The changes in spots seemed anything but slow, they drifted in irregular 

 ways, both in latitude and longitude, and when after disappearance they again 

 emerged at about the same region, the time was not sufficiently exact for 

 identification. So, as the attitude of a student towards all science should be one 

 of scepticism, following the advice of St. Paul to the Thessa'onians, ra^ra dt oo/.i- 

 fj.dc^Tz:, judge for yourselves about all things, I began to see if I could not ascertain 

 the exact period of solar rotation for myself, by less difficult and more certain 

 means than the observation of spots. I sought for and thought I had found it in 

 the periodicity of outbreaks of terrestrial magnetism. My theory was that the 

 internal convection-currents bringing intensely heated matter from the sun's 

 interior towards his surface would cause solar disturbance which in some way 

 would be radiated in pencils, like beams from search lights, from the sun to the 

 earth, that such convection-currents would follow established lines, and that 

 whenever the particular solar locality was turned towards the earth, there might 

 be a magnetic effect here, and surely would be, if at the time that solar volcanic 

 vent were active. I found from the whole series of Toronto observations, which 

 began in 1844, that one magnetic storm repeated, intermittently, but continuously 

 enough for a preliminary identification, in 27.24575 days synodical or 25.35447 

 days sidereal.* 



Two new announcements bearing on the subject were made about that time. 

 One was that cathode rays, which exist in abundance in solar radiations, carried 

 with them charges of negative electricity. Mr. H. Deslandres communicated to 

 the French Academy in 1898 bis discovery to that effect, and shortly afterwards it 

 was added that Leuard and Becquerel rays, emitted by radio-active substances, 

 have the same property. This solved the perplexing question, how could 

 electricity be radiated across space, in which there is no permanent conducting 

 medium. The other was that the spectroscopists, who have now perfected their 

 instruments so that they can tell the rate at which a luminous body is moving 

 towards or away from them, announced their agreement with the astronomers 

 who had been doubting the uniform rotation of solar spots. The sun being 

 two and a half millions of miles around, and rotating in 25 days, the velocity of 

 its rotatory movement at the equator is a mile and a ([uarter per second. Thus a 

 point at the equator is approaching us at that rate Avhen it comes into view, and 

 receding as it vanishes. The rates of approach and recession vary with the 

 distance from the equator of the locality under observation, but are quite 

 sufficient even near the poles to noticeably shift the dark lines of the solar 

 spectrum nearer to the blue end in the one case and to the red in the other. The 



* Transactions, Astronomical Society of Toronto, 1897. 



