126 



KNOWLEDGE. 



[June, 1903. 



Whether, however, evolution is the result of " natura 

 selcetiou." or any other form of whxt I take leave to caU 

 blind chance, is a totally different question, althovigh one 

 upon which I do not, on the present occasion, intend to 

 enter. 



THE ROTATIONS OF THE SUN, JUPITER, AND 

 THE EARTH, AND THEIR EFFECTS. 



By Mrs. Walter Maundek. 



In her latest and most valuable ■work, " Prolilems in 

 Astrophysics," Miss Gierke says : " The two fundamental 

 problems connected with the nature of the sun are its 

 rotation and its periodicity. They may be quite closely 

 allied, and in regard to both, 'counsels of despair' have 

 begun to prevail. The spot-cycle, like ' Cari-ington's law,' 

 is set down as a congenital peculiarity, and the mists of 

 the past are invoked to cover the perplexities of the present. 

 . . . Explanatory hypotheses aTail little, but the sifting 

 of facts avail much." Elsewhere, when dealing with 

 the " Structure and movements of sunspots," she wi-ites : 

 " Isolated observations are rarely of any considerable 

 value in such complex matters. Meaning accrues to them 

 just in proportion as they can be allied to others made in 

 correspondence with them, but under modified conditions. 

 ' Correlate and compare ' should be the watchword of 

 astrophysicists." In the following correlation and com- 

 parison I do not wish to suggest any explanatory hypothesis 

 whatsoever. I merely place in juxtaposition observations 

 of some phenomena that appear to be directly or indirectlv 

 allied. 



Again quoting from Miss Gierke, "Little progress 

 has been made towards ascertaining the cause of solar 

 periodicity. We are only assured that it is not im- 

 posed from without, but arises from within ; it resembles 

 a • free ' rather than a ' forced vibration.' This conclusion, 

 it is true, tends to relegate the matter to obscurity, for the 

 interior of the sun is a terra incognita, and seems likely to 

 remain so. His cyclical changes may belong to his original 

 constitution ; they may date from nebular times, and be as 

 inherent as the tone of a bell. Or they may simply 

 characterise a stage of growth, and prove liable to modifi- 

 cation and effacemeut." If the cause of the solar changes 

 is to l)e sought from the influence of something external— 

 of a planet or of several planets, for instance— then sooner or 

 later, the period, or the intermingled periods, must come 

 unravelled. If the primary cause lies within the solar 

 photosphere, then it may well be that the question is one 

 that our earthly experience may never enable us to answer ; 

 to even guess at the true answer. Or the hidden pro- 

 cesses may be modified by external influences, so that we 

 may be able to measure the method and extent of these 

 influences, and obtain an imperfect solution of the 

 problem 



In sheer ignorance we are obliged to postulate con- 

 duction and convection as the means of conveyiog heat 

 from the interior of the sun to his photosphere for radia- 

 tion. The processes of conduction proceed slowly ; there- 

 fore it is assumed that the sim is " a globe riddled with 

 convection currents of which the shining" cloud- shell of the 

 photosphere constitutes the limit." But convection is 

 impeded by viscosity, and this must increase as the tem- 

 perature and pressure together increase in the lower depths 

 of the sun. There must come a limit where convection 

 currents will cease to flow, and we cannot agree with Miss 

 Gierke that Dr. Wilsing and Prof. Sampson are wrong in 

 limiting " convective circulation within the solar glolie to a 

 relatively thin shell of material." In the deeper layers 

 there must be some other methods of transmitting thennal 



energy. In the " American Journal of Science " for 1902, 

 Prof. Frank Very advocated the theory that under the 

 transcendental conditions of the suns interior, heat is 

 evolved with explosive energy by the destruction of matter. 

 This can, however, scarcely be accepted as a working 

 hypothesis in a science that takes as its basis of argument 

 the conservation of energy and the conservation of matter. 



The condition of the sun's interior must prevail also 

 in Jupiter, though in a minor key. Here we have a 

 state of things that bears directly on the (juestion of the 

 solar surface markings, of their periodicity, and of their 

 connection with rotation. In January of the present year. 

 Prof. G. W. Hough published in " Science," N.S., Vol. 

 XVIL, No. 420, the results of his study of tlie planet 

 since 1879, and on this paper I base the facts and figures 

 hereafter given. 



It must be remembered that objects are very i-arely seen 

 beyond 40° of Jovian latitude. The latitude of 70^ is only 

 I" from the limb, and hence markings if they exist in such 

 a high latitude are practically invisible to us. Observa- 

 tions of Jupiter's surface are therefore almost entirely 

 confined to the eighty degrees that enclose his equator. 

 Within this region the markings consist of " white "' spots, 

 " dark ' sf)ots, and belts, all of which are disposed very 

 approximately along parallels of latitude. 



Many of these markings have a great degree of 

 permanence. The most famous, the Great Ked Spot, has 

 been identified with a great red sjjot observed by Hooke 

 and Gassini in 1664-6 ; it was then situated one-third of 

 the semi-diameter of the planet south of the equator in 

 about latitude 19°. It appeared and vanished eight times 

 between the years 166-5 and 1708, when it was invisible 

 until the year 1713. It became conspicuous in 1878, 

 since when it has been always visible, though at times so 

 faint as to be lost in small telescopes. This Jovian spot 

 difliers from its solar analogues in the degree of its 

 permanence. Like them, it is not stationary' in either 

 longitude or latitude, and a further similarity is that its 

 proper motion in longitude is much greater than its projier 

 motion in latitude. It has drifted in longitude about 

 three and one-fourth times ai-ound the planet since 1879 ; 

 its total displacement in latitude has been 1"'7, or about 

 4000 miles. Its rotation period is not unifonuly regidar. 

 From observations of Gledhill and Mayer, in 1869 and 

 1870, its period appeai'ed to be 9h. oom. 2.58s. ; in 1879, 

 Prof. Hough found it 9h. 55m. 33-7s. ; in 1898-9, 

 9h. 55m. 41-7s. ; and in 1902, 9h. 55m. 397s. Prof. 

 Hough is inclined to connect its visibility with its rotation 

 period. 



Prof. Hough differs from most other Jovian observers 

 in concluding that the rotation period of a spot does not 

 depend on its Jovian latitude. He cites the instance of 

 two white spots situated in latitude 6° south, which, from 

 1879 to 1885, gave a rotation period of 9h. 50m., the 

 equatorial belt giving at the same time a period of 9h. 55m. 

 The period 9h. 50m. is, indeed, more commonly found 

 between the limits —8° and -f 11°, whereas the longer 

 period is distributed indiscriminately over the surface 

 of the whole planet as far as 38 degrees latitude. The 

 diff'erence of rotation between two near- lying markings he 

 attributes to the dift'ereuce in their levels. We thus seem 

 to find an analogy to the different rotations given by 

 faculas and spots, but none to "Carrington's law of zones, " 

 — the different rotations given by spots in different 

 latitudes. 



Prof. Hough concludes his paper by saying : " It seems 

 to be the opinion of most writers on Jovian phenomena 

 that the planet is yet at a high temperature, but not self- 

 luminous. The high temperature is favourable for the 

 explanation of some of the phenomena observed. . . . 



