March 30, 191 1] 



NATURE 



h: 



is understood, we shall see that an " even-powered " stress 

 in the surrounding aether is necessarily involved. What I 

 do feel instinctively is that this is the direction for dis- 

 covery, that what is needed is something internal and 

 intrinsic, and that all attempts to explain gravitation as 

 due to the action of some external agency, whether flying 

 particles or impinging waves, are doomed to failure ; for 

 all these speculations regard the atom as a foreign sub- 

 stance — a sort of " grit " in the Eether — driven hither and 

 thither by forces alien to itself. When, some day, we 

 understand the real relation between matter and aether, I 

 iiture to predict that we shall perceive something more 

 nsfying than that. Oliver Lodge. 



University of Birmingham, March 25. 



Visual Sensations from the Alternating Magnetic 

 Field, 



\ There is no necessity to look to suggestion or other 



bstruse causes to account for this phenomenon. The 



Jectric currents induced in the head are quite sufliicient 



produce the effect. 



As I pointed out in a letter to The Electrician on April 



19 10, electrodeless currents in the body produced by 



:tromagnetic induction from a coil carrying so-called 



Jh-frequency currents have been in use in medical prac- 



for some years. 



Employing as primary a coil of wire of many turns, and 



le 2 feet in diameter, carrying high-frequency currents 



5m the discharges of a large battery of Leyden jars, and 



sing as secondary the body and the two arms bent so as 



form a circle, sufficient current can be induced in the 



rcuit formed by the arms and body to light a miniature 



^andescent lamp connected between the two hands, or a 



icient difference of potential can be produced between 



two hands to cause small sparks to pass visibly 



' ; ween them when they are held near together. 



It is easy to produce the visual flickering effect by pass- 

 i:ij4 through the head the current from an ordinary con- 

 tinuous-current magneto generator, such as is supplied with 

 the Evershed ohm-meter. One terminal of the generator 

 should be held in one hand, while a wire from the other 

 T.-rminal should be held in the other hand in contact with 

 -inall piece of wet sponge, and the latter pressed lightly 

 one side of the head just behind the eye. If the 

 aerator handle is then slowly turned (and it is wise to 

 n it slowly to avoid unpleasant results) the flickering 

 ■ -ct will at once become very noticeable, and as the 

 qucncy of the flicker increases with the speed of revolu- 

 n, it apparently is connected with pulsations in the 

 rrent due to the slow revolutions and the few segments 

 the commutator. The current through the head must 

 very small, as the bulk of that generated goes from 

 id to hand through the arms and body. 

 I first noticed this phenomenon some fifteen years ago 

 iiMi treating myself electrically for neuralgia, but I fancy 

 iit the effects of electric currents on vision have been 

 known much longer than that. 



Passing electric currents through the head in certain 

 directions also produces a metallic taste in the mouth. 



A. A. Campbell Swinton. 

 66 Victoria Street, Westminster, March 24. 



The Angular Speed of Rotation of a Long-enduring 

 Prominence. 



Thanks to the note contained in the " Astronomical 



^ vlumn " of Nature of March 9, my attention has been 



■ctcd to the very interesting article under the above 



iding in the January issue of the Astrophysical Journal. 



The proTiinence Mr. Evershed describes is the same as 



that under consideration in my letter contained in Nature 



■' February 23, and of which disc-spectrohcliograms were 



'^n in the issue of February 2 in connection with the 



[Hoduction of M. Deslandres' address of June 12, 1910. 



le Meudon spectroheliograms add thus a plate to 



•■•■ series enumerated by Mr. Evershed on p. 3 (Astro- 

 physical Journal, No. i, vol. xxxiii.), and an additional 

 date is further added by the spectroheliogram taken at 

 Meudon on April 15, 1910. Both arc beautifully repro- 

 'luced in the fine memoir forming vol. iv. of the Annales 



NO. 2 161, VOL. 86] 



of the Obs. d'Astr. Physique de Paris, of which M. 

 Deslandres is the author. 



The Meudon spectroheliograms seem greatly superior to 

 those accompanying Mr. Evershed 's article in the Astro- 

 physical Journal, undoubtedly on account of the excellent 

 and original instrumental combination resorted to by M. 

 Deslandres, which aims at the absolute isolation of the 

 central rays K, of calcium or of Ho of hydrogen. Com- 

 paring the Meudon spectroheliogram of March 21 with 

 what Mr. Evershed says (p. 5) as regards the appearance 

 of the dark formation under discussion, one cannot help 

 being struck by the seeming divergence of the evidence. 

 Mr. Evershed says : — " On March 21 it reappears as a 

 vague and ill-defined dark mass." Further, he states on 

 March 25 that " the northern arm can indeed be faintly 

 traced for a much greater distance in a vast circular sweep 

 towards the eastern limb." Reverting, now, to the 

 Meudon spectroheliogram of March 21, the dark mass is 

 seen of quite immense breadth longitudinally, no fewer 

 than 5 degrees, is pronouncedly distinct in its entire vast 

 extent also latitudinally, shows well-defined western and 

 eastern contours, both convex towards the west, and also 

 shows the narrow extension towards the N.N.E. quite 

 distinctly. This great difference of what the Kodaik^nal 

 plate for March 21 shows as compared with the plate 

 taken on the same day at Meudon, creates in my mind a 

 doubt as to the actuality of what Mr. Evershed suggests 

 on p. 6, viz. the disappearance in its entirety of the dark 

 formation between March 25 and 26. 



With due deference to the able observer, I venture to 

 say that possibly inaccurate relative setting of first and 

 second slits, along with insufficient dispersive power or 

 other optical inferiority to the Meudon spectroheliograph, 

 has not allowed the Kodaikdnal plates to be so sharp and 

 rich in detail as the Meudon plates. This is further sug- 

 gested by the striking absence on the Kodaikdnal plates of 

 many conspicuous dark calcium flocculi, which during 

 those days infested the sun's disc all over, yet, of course, 

 there is the possibility of their temporary absence ; but, 

 on the other hand, on each of the successive appearances 

 of the large prominence on the east or west limbs, the 

 formation exhibited the striking feature of a dark, flat 

 cloud hovering over the bright prominence-range along its 

 entire latitudinal extent, as described in my letter, suggest- 

 ing, therefore, continuity rather than intermittent or 

 " pufTing " action. The Meudon plate taken on April 15 

 clearly shows the re-entry into the disc of the dark forma- 

 tion, with a more acute apex directed towards the west 

 than during the previous transit, and the N.N.E. directed 

 arm is not yet absent as it is on the Kodaikdnal plate of 

 April 18. 



Incidentally, another exceptional feature of the sun's 

 disc should be mentioned which was strikingly on view 

 during April and May, 1910, viz. the fine circumpolar 

 wreath of dark flocculi in the south. A formation of this 

 kind goes a long way towards explaining the previously 

 puzzling experience of observing for many days- in 

 succession prominences at apparently the same position- 

 angles in comparatively low latitudes. These prominences 

 are, as a rule, of the quiescent, brushy, and rather dull 

 type. .Albert Alfred Buss. 



" Barrowdale," 22 Egerton Road, Chorlton-cum- 

 Hardy, Manchester, March 19. 



The Flow of Thin Liquid Films. 



In the very interesting letter by Mr. W. G. Royal- 

 Dawson in Nature of March 23 on the above subject, the 

 peculiar character of the stream-lines round a moving air 

 bubble compared with those round a fixed solid obstacle 

 may seem to some to require an explanation. As the 

 writer of the letter offers none, may I be permitted to 

 state what appears to be the cause of the conflicting 

 currents shown in Fig. 4 of Mr. Royal-Dawson's letter? 



It is stated that on pressing the cover-glass the bubble 

 seems to increase in size. From this we may conclude 

 that it is in contact with the glass surfaces top and 

 bottom. It will therefore be more or less anchored. The 

 result of this is that if it is to move it can only do so by 

 the formation of new film on the front, or by the old 

 film which is collecting in the rear from the top and 

 bottom of the bubble moving to the front. As water offers 



