52 



KNOWLEDGE 



[Makch 1, 1892. 



To tJic Eilitiir of Knowledge. 



SiK, — Having, duriug the past six years, devoted my 

 Observatory to the investigation of the light curves of 

 variable stars, I venture to draw the attention of your 

 readers to the following phenomena which I have not "seen 

 noticed elsewhere, except in the ease of the Nova Aurigw, 

 which was described in The Timn, 3rd inst., as "slightly 

 fuzzy " when first observed : — • 



I have given below extracts from my note book with 

 regard to three stars, and have, with my assistant, Mr. 

 (irover, frequently observed — 



(rt) A remarkably well-defined, almost planetary, disc. 



{h) A well-defined star, surrounded by a more or less 

 dense, ruddy atmosphere. 



(c) A large, woolly, ill-defined image, resembling a small 

 but bright planetary nebula. 



((/) At minimum, in place of the variable, a slight bluish 

 nebulosity. 



I do not consider that I have a sufficient series of 

 observations on which to base any theory, but trust that 

 other observers may be induced to take up what appears to 

 me to be an important field of enquiry. The telescope in 

 use is an achromatic of Gj inches aperture. 



Yours faithfully, 

 Eousdon Observatory, Devon, C'uthbekt E. Peek. 



February 17th, 1892. 



T. Cassiopeia. 1889, April 29tli. 7-9 mag. Very red, surroundctl 

 hy a ruddy haze in striking contrast to t)ie clear white of No. 6 

 (another star in the field). September 10th. TV mag. Verv red. 

 A well-defined star shining through a ruddy haze ("a" niglit; 

 mooidight). September 18th. 7-9 mag. Very red and hazy, ("a"* 



satellite) is not one fifteen-hundredth part as great as their 

 solar illumination, or the illumination derived from the 

 sun, which subtends an angle of less than 6' as seen from 

 the distance of .Jupiter's satellites, must be more than 

 1.500 times as great as that derived from the intrinsic 

 luminosity of the planet. I am therefore inclined to think 

 that C'apt. Noble's observation must isrobably be explained 

 as due to contrast or some other physiological cause. I 

 have been frequently struck by the amount of colour 

 visible on the disc of Jupiter as seen in an 18-inch silver- 

 ou-glass reflector. To my eye the body of .Jupiter shows 

 warm tints of red, canary colour, and blue, which are 

 very noticeable directly the attention is directed to the 

 colouring. — A. C. Ranyard.] 



[Having been kindly favoured by the editor with an 

 opportunity of reading the above note, I would merely say 

 that the tints of which he speaks on .Jupiter have their 

 ultimate origin in sunlight, as much as the red colour of a 

 holly berry or the yellow of a primrose has ; and that, 

 hence, such tints would be wholly invisible were the sun- 

 light cut ofl" from the surface emitting them by the shadow 

 of a satellite. I perhaps might have added to my original 

 .letter, that, during the visibility of the chocolate-coloured 

 shadow of Satellite II., that of Satellite I. was seen on 

 another part of the planet's disc, like a small circular spot 

 of the blackest ink. The fact that Mr. Campbell simul- 

 taneously saw (absolutely independently) the shadow of 

 the second satellite of the same colour as I did, surely 

 negatives any subjective cause of the phenomenon. A 

 physiological cause must, so to speak, be idiosyncratic. — 

 AV. Noble. 1 



S'7 mag. A large ill- 

 9'5 mag. Very red, and 



night). 1890, March 9th. 9 9 mag. . Very deep red, ill-defined. 

 (■' a " night.) October 16th. <i'6 mag. Large and ill-defined, 

 ("a" night.) 



R. Cassiopeia;. 1886, September 17tli. 

 defined deep red star. 1887, February 16tli 



not so shar|ily defined as the other stars in the field. March l:jtl 

 87 mag. Very red. Cannot bo focussed clear and sharp. September 

 19th. 7(5 mag. There is great ditllculty in getting a good image. 

 Tlie star seems as if snrrounded by a dense atmosphere. October 

 24.th. 72 mag. With power 136 it seems surrounded by an 

 atmosphere, or as if shining through fog. 1889, March 11th. 

 96 mag. Very hazy ami ill-defined as if shining through ruddy 

 mist. Other stars sharp. .July 21st. S'O mag. Exti'craely deep 

 ruddy. lU-defiued and liazy, quite unlike siu'roundiug stars. 

 ('• ■■^ " niglit-) 



S. Ilerculis. 1891, September 27th. 1.3 inag. A very minute 

 point. October 14th. No star visible witli powers 80 or s'-t. With 

 1.32 a faint nebulosity is suspected in the place of the variable ; on 

 slightly swaying the telescope a bluisli nebulosity is certainly seen. 

 October 28th. The nebulosity is best seen with power 136". The 

 minute stars near the place of the vai-iable .are well seen, clear and 

 sharp as usual. November 25th. Tlie variable has reappeared as 

 a minute but sharply-defined star. 



* Note.— Tlie letter " a " means a night of excellent definition. 

 Other stars with regard to which similar remarks appear in my note- 

 book, S. Cassiopeia?, &. Tauri, R. Aurigte, V. Cancri, E. Ursa; Majoris, 

 S. Ursfe Majoris, K. Camelopardi, R. Bootis, S. Corona>, R. Aq'uila' 

 S. Cephei. ^ 



[It is difficult to conceive of physical changes taking place 

 rapidly on the vast scale indicated by Mr. Peek and Mr. 

 Cxrover's observations. Possibly the blue nebulous haze 

 or corona round these variable stars may only become 

 visible to us when their light is small — as the variable star 

 increases inbrightness it seems possible that the light of 

 the star diffused in our own atmosphere may blot out or 

 eclipse the faint light of the nebula surrounding the 

 variable. 



During a total eclipse the light of the solar corona 

 becomes visible through the illuminated atmospheric veil 

 for the last few minutes before the " totality." If we could 

 suppose our sun to be a variable star, and its light to be 

 diminished till it eijuallcd that of the thin crescent of 

 photosphere left visible a few minutes before totality, we 

 should see the sinr under ordinary daylight conditions as 

 surrounded by the corona, but as the light of the solar disc 

 increased, the corona would be hidden by the solar light, 

 difi'used by our atmosphere, without any change neces- 

 sarily taking place in the brightness of the corona. — 

 A. C. Ranyabd.] 



THE CAUSE OF THK ICE AGE. 



To the Editor of Knowledge. 



Sir, — Since my letter on the cause of the Ice Age I have 

 seen Sir E. Ball's book on the subject, in which he cites 

 the passage (from 368c- of the Outlines) on which he relies 

 as establishing Herschel's inaccuracy. It is, no doubt, 

 carelessly worded, and goes some way towards justifying 

 the criticism, but I think the context shows that it was at 

 worst a slip of the pen. Sir John Herschel first gives the 

 usual explanation of the seasons, in which it is obviously 

 implied that each hemisphere receives less heat during its 

 winter than during its summer ; then he proceeds (S68ri), 

 " Let us now consider how these phenomena are woiHjied 

 by the ellipticity of the earth's orbit," &e. ; and in con- 

 sidering the modification, he does not again refer to this 

 unequal distribution of heat. In 368r, however, he says 

 that at the period of greatest eccentricity if the perihelion 

 took place at midwinter (for the northern hemisphere) " the 

 state of the two hemispheres would be strongly contrasted. 

 In the northern we should have a short but very mild 

 winter with a long but very cool summer, i.e., an approach 

 to perpetual spring ; while the southern hemisphere would 

 be inconvenienced and might be rendered uninhabitable by 



