No\-EMBER 1, 1895.] 



KNOWLEDGE. 



251 



Dr. Janssen has recently made an ascent to the 

 observatory on Mont Blanc, his object being to satisfy 

 himself concerning the safety of the new telescope which 

 has been conveyed to the observatory, and to inspect the 

 meteorograph which had ceased to be in working order. 

 He took the opportunity of observing the aqueous bands 

 in the solar spectrum. The air above him being very raie 

 and also extremely dry, he found that the bands at C and 

 D were absolutely invisible. Dr. Janssen already considers 

 it certain that there is neither oxygen nor aqueous vapour 

 in the solar envelopes. 



*-^-^ 



Two useful catalogues of scientific magic lantern slides 

 have been sent to us. The one from Messrs. Newton and 

 Co. contains among other things long series of slides on 

 astronomy, human physiology, hop culture, volcanoes, and 

 a new and useful series on British birds taken from 

 Mr. Lodge's drawings in Mr. Hudson's new book on the 

 subject. The other list, from Messrs. York and Son, 

 contains a number of good series on natural philosophy, 

 astronomy, mines, geography, and other subjects. 



A Frenchman, Mons. Dubois, has made an interesting 

 suggestion as to the origin of colour-blindness. This 

 defect of vision almost invariably consists in inability to 

 recognize red. Now a body cooling down from incan- 

 descence extends its spectrum towards the red end, or in 

 other words the white hot or violet-coloured body becomes 

 yellow and finally a dull red as it cools. A few stars such 

 as Sirius are white hot, many others like our sun are cooler 

 and therefore yellow, whilst others are so cooled down as 

 to shine with a dull red light. Primitive man, according to 

 Mons. Dubois, lived when the sun was in either the Sirius 

 or the pre-Sirius stage, that is, when the sun, which is the 

 source of all colour, was white hot, and had no red 

 component in its spectrum ; he had, therefore, no power of 

 recognizing red. Colour-blindness, therefore, says Mons. 

 Dubois, is merely atavism or degeneration to the primitive 

 type. The objection to this ingenious theory is that we 

 have no reason whatever for supposing that primitive 

 man was contemporary with a white hot sun ; further, 

 all white hot suns that we know of have some red at 

 any rate in their spectrum. The intensity of particular 

 components of the spectrum may vary, but the components 

 are still there. 



The fact that the coming total solar eclipse is visible so 

 near to us as Norway will doubtless induce a number of 

 people to journey there in August, IHOO. The Orient 

 Steam Navigation Company have already organized an 

 expedition to Yadsi). One of their steamers is to leave 

 London on July 21st, arriving at Vadau on August 8rd, 

 and leaving there on the luth is to be back again in 

 London on August 17th. Intending observers will do well 

 to take advantage of this comparatively inexpensive way 

 of travelling to and from the point of observation. 



1 ♦■« 



From observations at various high altitudes made last 

 year, and recently published, it has been found that the 

 quantity of solar radiation transmitted through the 

 atmosphere depends chiefly upon the tension of the 

 aqueous vapour, quite apart from the hygrometric state. 

 On fine days, with the same vapour-tension, the amount of 

 solar radiation transmitted is the same, but the amoimt 

 decreases rapidly as this tension rises and the amount of 

 vapour increases. With a perfectly clear sky the radiation 

 transmitted is greater when the sky is dark blue than when 

 it is light blue ; thus it is important when comparing 

 various observations on the heat from the sun, to determine 

 the colour of the sky by some accurate instrument. 



■We give our readers an excellent photograph of ribbon 

 lightning, taken by Mr. W. J. Bishop at Bath, on 

 August 22nd, 

 at 1.35 a.m. 

 The irregular 

 jagged course 

 through the 

 air of so- 

 called ribbon 

 lightning is 

 particularly 

 well-marked, 

 one side of 

 the ribbon 

 being much 

 brighter than 

 the other, 

 with a series 

 of brilliant 

 lines rimning 

 parallel to 



the bright edge, giving the flash the appearance of varying 

 greatly in vividness. This is much more apparent in the 

 orig'inal photograph, the engraving having suft'ered some- 

 what in detail by reproduction. 



VARIABLE RED STARS. 



By Dr. A. Bkester, Jun. 



THE atmospheres surrounding the glowing interior 

 of red stars contain, according to their spectra, 

 chemical compounds, and are, therefore, relatively 

 cool. If in these atmospheres some vapours are 

 cooled to their dew point, the stars, never ceasing 

 in their loss of heat by radiation, will cause those vapours 

 to condense in obscuring clouds, which will shut off the 

 light of the glowing interior and prepare a minimum 

 without the least change of temperature. 



These cool atmospheres, however, do not only contain 

 saturated vapours but also molecules (A and B) of 

 dissociated matter, cooled to a point, where their 

 recombination becomes possible. That recombination is 

 nevertheless impossible so long as the molecules A and 

 B are separated by too great a immber of other molecules 

 (E) with which they are mixed. For the same reason the 

 molecules O, and Hj of dissociated water do not recombine 

 when, as Deville has shown, they are mixed with a sutticient 

 quantity of carbonic acid.'' Now, as among these admixed 

 molecules R are also those of the saturated vapours indicated 

 here above, it is plain that their condensation into clouds 

 will rapidly diminish their number and cause the remain- 

 ing molecules E to become finally too few in number to 

 hinder the union of A and B any longer. 



Then at once, and as far as possible, these molecules 

 will unite, and the heat then produced will vaporize the 

 clouds of the minimum and restore the maximum by 

 opening again to view the constantly glowing interior of 

 the star. 



This rise to maximum, just like the fall to minimum, 

 happens without any change of temperature, for the heat 

 producing it, no matter how great it maybe, will be totally 



* Debrav : Diet, de Chimie, par A. Wurtz, Art. I)i3soeiation, p. 

 117-1. In'manT other cases a similar influence of admixed molecules 

 E has been observed as, e..<7.,in a mixture of H„ and 0„ when exposed 

 to light. The addition of molecules R then strongly diminislies the 

 rapidity of the combination. [Bunsen u. Eoscoe : Pogg. Ann. C, p. 

 ■13.] The current views as to electrolytical dissociation point also to 

 a similar influence of the water-molecules, preventing, when sufliciently 

 numerous, the separated ions from combining. 



