116 



KNOWLEDGE. 



[May 1, 18d4. 



that which surrounds the earth at a height of somewhere 

 about fiftj- miles above sea level, and that it is sufficiently 

 dense to vaporize meteoric showers. If this is so, should 

 we not see occasionally, either dm-ing observations made 

 with the telescope, or on photographs, some slight streaks 

 of light caused by a mass of meteorites, or a large aerolite, 

 passing obliquely across the dark portions of the moon's 

 surface ? 



Lewisham, S.E., Yours truly, 



April loth, 1894. A. E. Whiteuouse. 



[In the earth's atmosphere we only occasionally see 

 meteors which appear, as seen from a distance of one 

 hundred mUes, many times brighter than a star of the 

 first magnitude. As seen from a distance of one thousand 

 miles, such a meteor would only appear one hundredth part 

 as bright as when seen from a distance of one hundred miles ; 

 and when seen from the distance of the moon, the apparent 

 brightness of such a meteor would be reduced to less than 

 one five hundred millionth part of its brightness as seen 

 from a distance of one hundred miles, so that probably 

 the brightest meteors in the limar atmosphere would 

 escape attention, as seen from the earth. — A. C. E.\i;yAr.D.] 



To the Editor of Knowledge. 



Donville (Manche), France. 



Dear Sik, — Some doubts have recently been expressed 

 about the visibility of the whole ball of Venus, especially 

 when it has been observed during the daytime near to 

 inferior conjunction. 



I do not wish to state that the phenomenon is a real one, 

 but I would offer an observation which tends to show that 

 it is not an optical Ulusion. I was observing Venus on 

 January 24th, 1894, at Ih. p.m., and noticed that the 

 entire ball of the planet was vaguely seen, of an indefinable 

 colour, but it was impossible for me to ascertain if it was 

 brighter or darker than the surrounding sky. It was of 

 a kind of reddish-grey, and was much more visible with 

 the strong eye-pieces than with the weak (the eye-piece 

 principally employed magnified about two hundred and 

 forty times) ; that is to say, as the light of the sky grew 

 darker, by emploj'ing strong magnifying glasses, the ball 

 of the planet and its slightly difl'erent colour fi-om the sky 

 became more marked. Would not an optical illusion, on 

 the contrary, be more visible with a weak eye-piece — that 

 is to say, one giving a brilhant image ? 



I am, dear Sir, yours truly, 



L. EUDAUX, 



Membre de la Societe Astronomique de France. 



[The higher magnifying power would, of course, decrease 

 the light derived from the body of the planet just in the 

 same proportion as it decreased the light derived from the 

 sm-rounding sky ; but the contrast may appear more evident 

 when the brightness of both areas is decreased. I feel no 

 serious difiiculty in assuming that the body of Venus may 

 shine, when it is not illuminated by the sun, with a light 

 which is comparable in brightness with the light derived 

 from the dust in the earth's atmosphere, when illuminated 

 by the sun's rays. This dust forms a semi-transparent 

 veil, sufficient to hide the planets when looked for with the 

 naked eye, but not sufficient to hide them in the tele- 

 scope. 



On the 24th of .January, about one-seventh of the disc of 

 Venns was illuminated by the sun. A curious fact is that 

 the phenomenon observed by M. Kudaux seems to become 

 more and more apparent as the planet approaches the 

 sun, and is seen through the brighter parts of the atmos- 

 pheric veil, for the general brightness of the sky increases 

 rapidly as we approach the sun. 



I have on more than one occasion, when Venus has been 

 nearer to the sun than it was on the 24th of January, 

 seen what appeared to me to be the whole body of the 

 planet, clearly distinguishable on the background of 

 sky. It may be that the light from the illuminated 

 crescent of Venus lights up the dust in our atmosphere in 

 the immediate neighbourhood of the planet's place, so as 

 to render it more opaque than it is rendered by the less 

 direct illumination of the sun's rays. The patch of 

 illuminated atmosphere roimd the brighter stars is well 

 known to all telescopic observers. With a large instru- 

 ment, the brightened appearance of the sky before a 

 large star enters the field of the telescope has been 

 frequently compared to the light of approaching dawn. 

 — A. C. Ran YARD.] 



THE AURORA AND ZODIACAL LIGHT. 

 To the Editor of Knowledge. 



Deak Sir, — The zodiacal light has been a prominent 

 object every clear evening of the first three months or so of 

 each year I have spent here — nearly twenty of them. 

 December 17th is, I think, the earliest date I have seen it, 

 and I do not remember it later than the middle of April, 

 with very varying extension. For the first time, yesterday 

 I saw it in daylight, i.e., immediately after stmset, of a 

 pretty rose-colour, somewhat like the wondrous after-glows 

 of ten years ago, but distinct in this respect, that those 

 generally had the sun's place for centre, whereas this had 

 not, but was an oblong, rounded mass, with its major axis 

 lying along the ecliptic. 



About 9.30 I fotmd an ain-ora pervading the northern sky, 

 chiefly in the true (not magnetic) north ; low down pale 

 green, then- a bank of cloud, and above that, to within 

 ten degrees of Polaris, rose-colour, with shootings of 

 pencilled rays, and the complementary colours thus evenly 

 distributed above and below the nimbus. These colours 

 lasted only a short time, but aU night I suppose (at least 

 till 2 a.m.) the whole lower northern sky was brilliant with 

 yellow radiance, like a summer dawn or early night, but its 

 centre was the magnetic north. Its beauty was much 

 enhanced by masses of cloud (looking black like nimbus, 

 though probably they were only cumulus). 



The zodiacal light is usually supposed to belong to the 

 sun, the aurora borealis to the earth ; yet last evening's 

 displays seemed to point to a real connection or sympathy, 

 such as is also pointed to by the connection between solar 

 disturbance and magnetic storms. May not the sun's 

 corona extend in an invisible, attenuated condition beyond 

 our own orbit, so that we are always within it, but when 

 the sun is more than usually active we see it at our poles as 

 well as along the ecliptic '? Would not this explain what 

 now seems inexplicable, viz., the immediate magnetic 

 sympathy between the earth and the sun '? 



I once asked Mr. Proctor to give us a monograph on 

 the zodiacal light, putting together all the known facts and 

 probable theories. I wish that I could induce you to take 

 the matter up. Yours faithfully, 



A. P. Skene. 



Pornic, Loire Inf., France, March 31st, 1894. 



[I am collecting facts with regard to auroral displays, 

 which I hope to put together for publication. I have 

 recently had an opportunity of examining some very 

 interesting photographs of the aurora, taken during the past 

 year by Dr. Martin Brendel. I may, perhaps, be allowed 

 to reproduce them in Knowledge. Mr. Skene wiD find a 

 short paper " On the Connection between Sunspots and 

 Magnetic Storms" in Knowledge for April, 1892. I still 

 hold to the theory there advocated. It assumes that 



