September 5, 1S84. 



SCIENCE. 



199 



equatorial acceleration is a most important one 

 and still unsolved. Probably its solution depends 

 in some way upon a correct understanding of the 

 exchanges of matter going on between the inte- 

 rior and the surface of the fluid, cooling globe. It 

 is a significant fact (already alluded to), that a similar 

 relation appears to hold upon the disk of Jupiter; the 

 bright spots near the equator of the planet complet- 

 ing their rotation about five minutes more quickly 

 than the great red spot which was forty degrees from 

 the equator. It is hardly necessary to say that an 

 astronomer, watching our terrestrial clouds from some 

 external station (on the moon, for instance), would 

 observe just the reverse. Equatorial clouds would 

 complete their revolution more slowly than those in 

 our own latitude. Our storms travel toward the east, 

 while the volcanic dust from Krakatoa moved swiftly 

 west. We may at least conjecture that the differ- 

 ence between different planets somehow turns upon 

 the question, whether the body whose atmospheric 

 currents we observe is receiving more heat from 

 without than it is throwing off itself. Whatever 

 may be the true explanation of this peculiarity in the 

 motion of sun-spots, it will, when reached, probably 

 carry with it the solution of many other mysteries, 

 and will arbitrate conclusively between rival hypothe- 

 ses. 



The periodicity of the sun-spots suggests a number 

 of important and interesting problems; relating, on 

 the one hand, to its mysterious cause, and, on the 

 other, to the possible effects of this periodicity upon 

 the earth and its inhabitants. I am no ' sun-spottist ' 

 myself, and am more than sceptical whether the 

 terrestrial influence of sun-spots amounts to any 

 thing worth speaking of, except in the direction of 

 magnetism. But all must concede that this is by 

 no means yet demonstrated (it is not easy to prove 

 a negative); and there certainly are facts and 

 presumptions enough tending the other way to 

 warrant more extended investigation of the subject. 

 The investigation is embarrassed by the circumstance, 

 pointed out by Dr. Gould, that the effects of sun-spot 

 periodicity, if they exist at all (as he maintains they 

 do), are likely to be quite different in different por- 

 tions of the earth. The influence of changes in the 

 amount of the solar radiation will, he says, be first 

 and chiefly felt in alterations and deflections of the 

 prevailing winds, thus varying the distribution of 

 heat and rain upon the surface of the earth without 

 necessarily much changing its absolute amount. In 

 some regions it may, therefore, be warmer and dryer 

 during a sun-spot maximum, while in adjoining- 

 countries it is the reverse. 



There can be no question, that it is now one of the 

 most important and pressing problems of observa- 

 tional astronomy to devise apparatus and methods 

 delicate enough to enable the student to follow 

 promptly and accurately the presumable changes in 

 the daily, even the hourly, amounts of the solar radi- 

 ation. It might, perhaps, be possible with existing 

 instruments to obtain results of extreme value from 

 observations kept up with persistence and scrupulous 

 care for several years at the top of some rainless 



mountain, if such can be found; but the under- 

 taking would be a difficult and serious affair, quite 

 beyond any private means. 



Related to this subject is the problem of the con- 

 nection between the activity of the solar surface and 

 magnetic disturbances on the earth, — a connection 

 unquestionable as matter of fact, but at present un- 

 explained as matter of theory. It may have some- 

 thing to do with the remarkable prominence of iron 

 in the list of solar materials; or the explanation may, 

 perhaps, be found in the mechanism by means of 

 which the radiations of light and heat traverse inter- 

 planetary space, presenting itself ultimately as a 

 corollary of the perfected electro-magnetic theory of 

 light. 



The chromosphere and prominences present several 

 problems of interest. One of the most fruitful of 

 them relates to the spectroscopic phenomena at the 

 base of the chromosphere, and especially to the strange 

 differences in the behavior of different spectrum- 

 lines, which, according to terrestrial observations, 

 are due to the same material. Of two lines (of iron, 

 for instance) side by side in the spectrum, one will 

 glow and blaze, while the other will sulk in imper- 

 turbable darkness ; one will be distorted and shattered, 

 presumably by the swift motion of the iron vapor to 

 which it is due, while the other stands stiff and 

 straight. 



Evidently there is some deep-lying cause for such 

 differences; and as yet no satisfactory explanation 

 appears to me to have been reached, though much 

 ingenious speculation Las been expended upon it. 

 Mr. Lockyer's bold and fertile hypothesis, already 

 alluded to, that at solar and stellar temperatures our 

 elements are decomposed into others more elemental 

 yet, seems to have failed of demonstration thus far, 

 and rather to have lost ground of late; and yet one 

 is almost tempted to say, 'It ought to be true,' and 

 to add that there is more than a possibility that its 

 essential truth will be established some time in the 

 future. 



Probably all that can be safely said at present is, 

 that the spectrum of a metallic vapor (iron, for in- 

 stance, as before) depends not only upon the chem- 

 ical element concerned, but also upon its physical 

 conditions ; so that, at different levels in the solar at- 

 mosphere, the spectrum of the iron will differ greatly 

 as regards the relative conspicuousness of different 

 lines; and so it will happen, that, whenever any mass 

 of iron vapor is suffering disturbance, those lines 

 only which particularly characterize the spectrum of 

 iron in that special state will be distorted or re- 

 versed, while all their sisters will remain serene. 



The problem of the solar corona is at present 

 receiving much attention. The most recent investi- 

 gations respecting it — those of Dr. Huggins and Pro- 

 fessor Hastings — tend in directions which appear to 

 be diametrically opposite. Dr. Huggins considers that 

 he has succeeded in photographing the corona in 

 full sunshine, and so in establishing its objective 

 reality as an immense solar appendage, sub-perma- 

 nent in form, and rotating with the globe to which 

 it is attached. One may call it ' an atmosphere, 5 if the 



