March 8, 1900] 



NATURE 



443 



LETTERS TO THE EDITOR, 



f The Editor does not hold himself responsible for opinions ex- 

 pressed "by his correspondents. Neither can he undertake 

 to return^ or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. '\ 



The Structure of the Inner Corona. 



It was my good fortune to observe the total eclipse of 1878 

 at the very exceptionally favoured station of Pike's Peak, at an 

 elevation of 14,000 feet, and in the clearest air. 



Having a few months earlier, on the occasion of the transit of 

 Mercury, of May 6, been enabled to see the planet before it 

 reached the sun's limb, owing to its projection on the back- 

 ijround of the inner corona, I was greatly impressed by the 

 brightness of the latter close to the sun, and though unable to 

 give it more than a few seconds' visual observation during the 

 eclipse, this was done with a five-inch achromatic, with a 

 magnifying power of 72, which, so far as I know, gave the 

 earliest intelligence of the extraordinary structure which obtains 

 there. 



I quote from my report addressed to the Superintendent of 

 the United States Naval Observatory, and published in the 

 Annals of the Observatory for 1876 (Appendix iii. p. 209) : — 



" What I saw thus momentarily was not in (he least what I 

 expected. If there were any structure in the very inner corona, 

 it had escaped me when I had searched for it in a previous 

 eclipse (at Jeres, in 1870). It is true- that the sky was hazy on 

 that occasion, and that on this it was exquisitely clear. Now 

 what I saw in this brief view was a surprisingly definite fila- 

 mentary structure, somewhat coarser and decidedly more 

 sharply defined than I have ever seen filaments in the photo- 

 sphere, not disposed radially, or only so in the rudest sense, 

 sharpest and much the brightest close to the disc, fading rapidly 

 away into invisibility at a distance of five minutes of arc or more 

 <possibly in some cases of ten). The salient point to me was 

 this very remarkable definiteness and precision of these forms, 

 and this impression, made on my mind in that too brief moment, 

 is reproduced in this sketch {not here given), taken from one 

 made within ten minutes of the event. It is in no way a 

 ' picture,' but a reproduction of the original memorandum of the 

 first impression of the features of the (telescopic) inner corona, 

 which were, to repeat : (i) Extraordinary sharpness of fila- 

 mentary structure ; (2) arrangement not radial, or only so in 

 ; he rudest sense ; (3) generally curved, not straight lines; (4) 

 curved in different directions ; {5) very bright close to the edge, 

 and fading very rapidly, — fading out wholly at from five to ten 

 minutes from it." 



If I can trust to this memorandum of an observation which, 

 however brief, was made under uniquely favourable circum- 

 stances, and to my own recollections, I should say that while 

 most interesting photographs of the inner coronal structure have 

 recently been made, yet that this feature has not yet been done 

 justice to even in the best of them I have seen, and that it 

 perhaps cannot be, with our present means. While trusting 

 then that at the coming eclipse it will be a prominent subject 

 for every party with an adequate photographic outfit, I beg to 

 express the hope that wherever possible it may be made the 

 subject of telescopic visual study. S. P. Langley. 



Smithsonian Institution, Washington, February 23. 



^Suggested Source of the Energy of the " Becquerel 

 Rays." 



In view of the difficulties arising in supposing that the energy 

 to produce the photographic, ionising and phosphorescent 

 screen effects with the "Becquerel Rays," continuously eman- 

 ates from the active substance, I would suggest that the possi- 

 bility should be kept in view of the real source of the energy 

 being found in the things themselves in which these effects are 

 manifested. 



From this point of view the emanating influence would be 

 looked upon rather in the light of lines of force than as a wave 

 propagation ; and, indeed, up to the present we have no con- 

 clusive evidence that the effects are those of waves. 



The ionising power is especially suggestive, and considered 

 in connection with other known ionising effects through 

 molecular distances, may well be only the case of similar 



NO. 1584, VOL. 61] 



action taking place over greater ^{listances, corresponding to 

 centres of greater molecular mass, such as the atomic weights of 

 those up to the present observed active substances possess. 

 The effect would then be viewed as due to what might be called 

 a Becquerel field of force, arising it may be from some strained 

 condition of the ether directly accompanying the existence of 

 material molecules, or through the intermediary action of 

 molecular chains. In this connection, as well as on account of 

 the magnetic deflection, it would be important to know if the 

 action takes place through a really high vacuum. 



From this view the active substance need not lose in power 

 with time, and so long as fresh unused-up material to be acted 

 upon is brought up there need be no cessation in the effects 

 observed. 



An observation of M. and Mdme. Currie that a phosphorescent 

 screen ceased to afford illumination after a time, although the 

 active substance continued to effect fresh screens is in agree- 

 ment wiih this, as well as their further observation that the 

 exhausted screen after exposing to light is again capable of 

 being effected. Thus some of the energy, at least if not all, is 

 apparently to be attributed to the screen. 



The effect, then, would be looked on as one of chance align- 

 ment or directive selection in a field of force ; advantage, so to 

 speak, being taken of suitable molecular movements according 

 as they occur in the effected matter. 



Yrom this point of view there would be a close analogy with 

 the action which takes place in a piece of soft iron in the field 

 of a permanent magnet. The process of gradual orientation of 

 the molecules in the iron, while it is occurring, corresponding 

 to, say, the luminous stage in the phosphorescent screen. The 

 final stage of magnetisation corresponds to the exhausted 

 condition of the screen. 



If these suggested views were correct we might expect from 

 the analogy that forces should exist between the acted-on sub- 

 stance and the source of the " Becquerel Rays." 



Fred. T. Trouton. 



Physical Laboratory, Trinity College, Dublin. 



A Possible Cause of the Variability of Stars. 



In our study of nature it is sometimes advantageous to 

 speculate as to possible causes of observed phenomena in cases 

 where we are not yet in a position to institute an investigation 

 which would entitle us to have no doubt as to the true cause. 

 The cause suggested by the speculation may possibly prove to 

 be the true cause ; and if not, it is at all events likely to bear 

 a valu?>ble analogy as regards the laws of its operation, with the 

 mode in which the real cause operates. 



Prof. George Darwin's theory as to the origin of the moon 

 is one of the most striking examples of such a specu- 

 lation ; and it was on reading it some years ago that an 

 application of the same principles of action to account for 

 variable stars occurred to the present writer. He now pub- 

 lishes the speculation because it seems to offer a satisfactory 

 explanation of some remarkable facts recently brought to light 

 which have attracted much attention, viz. that as many as forty 

 stars of the Cluster Messier V., nearly one-twentieth of «11 the 

 stars in the cluster, have been found to be variables possess- 

 ing periodic times, light-curves, maxima of brightness, and 

 minima of brightness, which, though not the same, do not 

 differ much from one star to another. 



As an introduction to the explanation which is about to be 

 suggested, it will be convenient to refer to a very early ex- 

 perience of the writer. Potatoes used formerly to be boiled in 

 open pots over a naked fire, and a phenomenon then presentea 

 itself, which he often watched when a boy with wonder, until 

 at length, to his satisfaction, he perceived the very simple 

 cause to which it is due. The water at almost equal intervals 

 of time swelled up, and a little boiled over ; it then subsided 

 and boiled more tranquilly. These phases were repeated with 

 surprising regularity, making the whole a definite quasi-periodic 

 phenomenon ; although upon a closer scrutiny it was found 

 that the intervals, while nearly, were not exactly equal, neither 

 were the recurring phases of the phenomenon accurately alike. 

 Further experience showed that this example of quasi-periodicity 

 is not exceptional, but one of a great body of quasi-periodic 

 phenomena which occur in nature. With one of them we are 

 here concerned, viz. with that which goes through its evolutions 

 upon our sun, and manifests its approximately periodic character 

 in the eleven-year period of sun-spot frequency. 



