296 



NATURE 



\7uly 28, 1 88 1 



travels were much impeded by a revolution among the natives 

 and the prolonijed drought. Nevertheless four cases, contammg 

 collections of seeds, plants, reptiles, insects, and mollusks, have 

 arrived at Frankfort, and Dr. Kobelt has obtained valuable 

 results concerning the geographical distribution of mollusks. 

 With regard to the revolution among the Arabs it appears that 

 they are°of opinion that the fifty years during which the Prophet 

 has permitted the French to hold Algiers are now over. Dr. 

 Kobelt has left for Spain, where he will continue his researches 



We are informed that Mr. J. M. Schuver, the adventurous 

 Dutch traveller, who not long ago started on his formidable 

 journey from Cairo to the Cape, is not at Famaka, on the 

 southern frontier of Fazokl, as has been stated, but has esta- 

 blished his headquarters for the present a considerable distance 

 to the south, and actually in the Galla country. A quantity of 

 stores have la'ely been sent from London to Fazokl for him by 

 way of Suakim, and it is Mr. Schuver's intention to return to 

 Fazokl for them in November next, before proceeding on his 

 southward journey. In the meantime he has established a 

 dromedary post between his camp in the Galla country and 

 Khartum. 



In the luly number of Petennann's Mittheilungen Lieut. 

 Kreitner describes at considerable length the observation made 

 by him while in company with Count Szechenyi, journeying from 

 Sayang in Yunnan to Bhamo in Burmah ; a useful map accom- 

 panies the paper. Dr. Junker continues his letters describing his 

 travels in the Niam-Niam country, concluding with some im- 

 portant observations on a visit he paid to some of the Monbuttu 

 tribes. Dr. Kadde concludes the narrative of his journey to 

 Talysh, Aderbejan, and Savulan. 



We have received from Perthes of Gotha parts 23 to 26 of 

 the new editim of Stieler's Hand-Atlas. This edition has con- 

 tinued to appear with praiseworthy regularity, and will be com- 

 pleted in other sbc parts. 



Among the papers in No. 20 of the Bulletin of the I,yons 

 Geographical Society are the following :— The Economic Unity 

 of the Globe, by Prof. C. Stewart Merritt ; the South Pole, by 

 M. E. Cha iibeyrin ; the Slave Coast, by Dr. Chappet ; South 

 Africa, a lecture by the Rev. M. Coillaird, the missionary who 

 succeeded Serpa Pinto ; Lake Fucino, by M. Math. Desgrands. 



The U.S. steamer Alliance, in search of the Jeanette expe- 

 dition, arrived at Hammerfest on its way to the Siberian Arctic 

 Seas on the 24th inst. 



The Egyptian Geographical S iciety does not often issue a 

 Bulletin, but when it does the number usually contains some 

 g )od matter, often drawn from the archives of the General Staff, 

 the chief of which is President of the Society. The number 

 just publi hed contains, among other matter, a paper on Cape 

 Guardafui by Col. J. Graves of the Staff, and another on .the 

 country between the coast and the lofty plateau of Abyssinia by 

 Gen. Stone Pasha. 



Commandant Titre, who was formerly at the head of the 

 Survey Department in Algiers, has lately published a large ma)) 

 of Algeria, which embodies all the most recent topographical 

 information. 



SOLAR PHYSICS— THE CHEMISTRY OF THE 



SUN^ 

 '\\J'£ have next to consider another method, which enables us 

 ■ to determine the motions of the solar gases. It has been 

 already noticed that it is easy to see the pr eminences rushinj; with 

 extreme velocity upwards in radial lines from the photosphere, 

 and that while they are thus being carried up by same violent 

 motion of ejection fiom below, they are twisted out of the radial 

 line, now to the right, and now to the left, by what we are 

 justified in describing as winds in the atmosphere of the sun. 

 Those were the mere viual phenomena which were incidentally 

 observable the moment a method was obtained of viewing the 

 forms of prominences as well as the bright line; produced by the 

 vapours of which they were built up, and they afforded us an 

 opportunity of getting an insight into solar meteorology. 



It was soon however perfectly clear that there was another 

 method, in some respects a much better method, of doing this 

 work. When we consider how it hrppens that we get any 



' Lectures in the Course on Solar Physics at South Kensington (see p. 150)' 

 Revised from shorthand notes. Continued from p. 274. 



phenomena visible in our u liverse at all, we are driven to the 

 conclu ion that it depends on the fact that bodies in a state of 

 agitation reflect, so to speak, their own state of agitation on the 

 ether, and that the ether carries those vibrations, those agitations 

 to our eyes. So that if we can assume, as we must assume, 

 that the sun with its gases, consisting of hydrogen, magnesium, 

 &c., was communicating its vibrations to the ether, and the ether 

 was communicating in its turn its vibrations to us, it was obvious 

 we had there an opportunity of testing a view which had been 

 put forward by Doppler a good many years ago, to the effect that 

 the light from a moving light source is not the same in all its 

 qualities as light from a fixed one. 



The colours which we see in the spectrum are exactly 

 analogous to the notes which we hear in a piano when we 

 go from one end of the scale to the other. D:)ppler ima- 

 gined the equivalent of a piano going away from or coming 

 towards the listener with considerable velocity — a velocity 

 comparable, in fact, to the velocity of sound through the air. 

 It is perfectly clear that under these circumstances we should 

 no longer get true concert pitch, for the reason that the note 

 which gives us a certain tone, because it produces in the 

 air so many waves per second, will change its tone if the source 

 of the note is coming to us. Take, for instance, a tuning-forlv 

 giving concert C, and imagine it rapidly coming to us : the waves 

 of sound will be crushed together, we shall have more waves in 

 a second falling on the ear, and we shall get a higher note. If 

 we imagine, on the other hand, the tuning-fork is going away 

 from us, the notes \\ill be paid out at longer intervals, so to 

 speak, and we shall get a lower note. In neither case shall we 

 continue to have concert C. A very familiar instance where we 

 do get thi< change of pitch due to change of motion, is produced 

 in the e daj's of very rapid railway travelling. Any of us who 

 have been at a country railway station when the express is coming 

 by will kn iw that as the train approaches us the note of its 

 whistle is at one pitch, and as it goes from us after passing 

 it changes and gets lower, according to the velocity of the train. 

 A familiar experimental illustration of this principle is to 

 attach a whistle to the end of a long india-rubber tube. If then 

 a person -rounds the \^'histle by blowing through the open end 

 of the tube, and w-hile still blowing whirls it round rapidly in a 

 vertical plane in which an obicrver is standing, that observer will 

 note that when the whistle is approaching him in one part of the 

 curve, and the waves are therefore being crushed together, the 

 note will appear higher than when it is receding from him in the 

 opp )site part of the curve, where the waves are being, as it were, 

 pulled asunder. Now apply that to the lii^ht of the sun. The 

 long notes of light are red, and the short notes are blue, and it 

 we sharpen or shorten any light note in any part of the spectrum 

 we shall give that light a tendency to go towards the b'ue, and 

 if we lengthen or flatten it we shall give it a tendency to go 

 towards the red, so that, for instance, if a mas; of magnesium gas , 

 giving the line or note in the green indicated by "b" is approach- 

 ing us with a vel.ici'y comparable to the velocity of I'ght, the 

 line will change its position in the spectrum towards the blue ; 

 and if we are careful to note the exact amount of change of 

 refrangibility as it is called, we shall have then an absolute 

 method of determining the rate of motion of that mass of gas. 

 This will help us in more ways than one. Suppose we observe 

 the gas at the limb of the sun, we shall then, if we get any 

 chnnge of refrangibility, be justified in calbng it a solar wind, 

 because the motion thus indicated would be very nearly parallel 

 to the surface of the sun ; but if on the disk of the sun itself — 

 t.ake a spot, for instance, in the very middle of the disk — we get 

 any change of wave-length such as I have referred to, it is 

 perfectly clear that we shall no hniger be dealing with what we 

 can justly call a wind, it will really be an upward or downward 

 current. So that this principle enables us at the limb of 

 the sun to determine the velocity of solar winds, and at the 

 centre of the sun to determine the velocity of those up-ru-hes or 

 down-rushes, in fact, those convection currents to which Prof. 

 Stokes has already directed attention. 



The accompanying drawings (Fig. 16) were made when the sun 

 was in a considerable state of agitation in the year 1S72. They 

 give us one of the lines of hydrogen, and indicate, I think, amply 

 this kind of phenomenon. We have in the first figure on a large 

 scale the "F" line of hydrogen, the line in the green at the edge 

 of the sun. The slit — the perfectly straight slit — has been worked 

 round the limb in search of a prominence, and it has found one. 

 But the slit is no longer shown us as a perfectly straight line, it 

 is in fact a very irregular one ; and further than this it branches 



