4i6 



NATURE 



\_Scpt. 2, iSb'o 



or when raised to the highest temperature by burning the 

 cyanogen in nitric oxide ; but no flames appear to give these 

 tands unless tlie burning substance contains nitrogen already 

 united with carbon. As the views of Mr. Lockyer witli 

 regard to the multiple spectre of carbon have very recently 

 appeared in the pages of Nature, I need only say that 

 the?e spectra are looked upon as supporting his theory that 

 the different flutings are truly due to carbon, and that they 

 represent the vibrations of different molecular groupings. The 

 matter is one of very great interest as regards the spectra 

 of comets, for the bands ascribed to acetylene occur in the 

 spectra of comets without the bands of nitrogen, showing 

 that either hydrocarbons must exist ready formed in the 

 comets, in which ca-e the temperature need not exceed that 

 of an ordinary flame, or else nitrogen must be absent, as th e 

 temperature which would produce acetylene from its elements 

 would also produce cyanogen, if nitrogen were present. 



Quite recently, Professors Liveing and Dewar have, simultan- 

 eou^ly with Dr. Huggins, described an ultra-violet emission 

 spectrum of water, and have given maps of this spectrum. 

 It is not a little remarkable that by independent methods these 

 observers should have deduced the same numbers for the wave- 

 lengths of the tno strong lines at the most refrangible end of 

 this spectrum. 



Great attention has been paid by M. Mascart and by M. 

 Cornu to tlie ultra-violet end of the solar spectrum. M. 

 Mascart ^\as ab'e to fix lines in the solar spectrum as far 

 as the line R (3179), but was stopped by the faintness of 

 the photographic impression. Prof. Cornu has extended the 

 spectrum still farther to the limit (2948), beyond which no 

 further effect is produced, owing to complete absorption by 

 the earth's atmosphere. A quartz-reflecting prism was used 

 instead of a heliostat. The curvature of the quartz lens was 

 calculated so as to give minimum aberration for a large 

 field of view. The Iceland spar prism was very care- 

 fully cut. A lens of quartz was employed to focus the sun on 

 the slit. Having photographed as far as possible by direct 

 solar light. Prof. Cornu compared the solar spectrum directly by 

 means of a fluorescent eye-piece with the spectram of iron, and 

 then obtained, by photography, the exact positions of the iron 

 lines which were coincident with observed lines in the solar 

 spectrum. M. Cornu states that the dark absorption lines in the 

 sun and the biigh* iron lines of the same refrangibilityare of the 

 same relative importance or intensity in their spectra, indicating 

 the equality between the emissive and the absorbing powers 

 of metallic vapours ; and he thinks that we may get by 

 the comparison of bright spectra with the sun some rough 

 approximation to the quantity of metallic vapours present 

 in the absorption layers of the sun's atmosphere. He 

 draws attention to the abundance of the magnetic metals — 

 iron, nickel, and magnesium — and to the fact that these 

 substances form the composition of most meteorites. M. 

 Cornu has studied the extent of the ultra-violet end of the 

 spectrum, and finds that it is more extended in winter than in 

 summer, and that, at different elevations, the gain in length of 

 the spectrum for increase of elevation is very slow, on account of 

 atmospheric absorption, so that we cannot hope greatly to extend 

 the spectrum by taking elevated observing stations. The limit 

 of the solar spectrum is reached very rapidly, and the spectrum 

 is sharply and completely cut off at about the line U (wave length 

 2948). From photographs taken at Viesch in the valley of the 

 Rhone, and at the Rifielberg, 1910 metres above it, M. Cornu 

 finds the limits to be at wave-lengths 2950 and 2930 respectively. 

 In the actual absorption of bright-line spectra by the earth's 

 atmosphere, M. Cornu observed among others three bright-lines 

 of aluminium, which M. Soret calls 30, 31, and 32 (wave-lengths 

 about 198S, 1930, and 1S60), and he found that 32 could 

 not be seen at the distance of 6 metres ; but on using a col- 

 limator and reducing the distance to li metres, the line 32 

 became visible, notwithstanding the abs'orption of the extra 

 lens ; at i metre, line 32 was brighter than 31, and at a 

 quarter of a metre 32 was brighter than either 30 or 31. 

 \\'ith a tube 4 metres in length between the collimator and 

 prism ray 32 is not seen ; but when the tube is exhausted, ray 

 31 gains in intensity and 32 comes into view, and gradually gets 

 brighter than 31, whilst 30 changes very little during the ex- 

 haustion. With the same tube he found no appreciable differ- 

 ence between the absorption by air very carefully dried and by 

 moist air, and concludes that this absorption is not due to the 

 vapour of w ater, and it follows the law of pressure of the atmo- 



sphere which shows it to be due to the whole mass or thickness 

 of the air. Also, M. Soret has shown that water acts very 

 differently on the two ends of the spectrum, distilled water being 

 perfectly transparent for the most refrangible rays, since a 

 column of water of 116 cm. allowed the ray 2060 in the spec- 

 trum of zinc to pass through ; on the other hand, water is so 

 opaque to the ultra-red rays that a length of I cm. of it re- 

 duces the heat spectra of metals to half their length and one 

 quarter of their intensity. 



In concluding my address, I wish to draw attention to some of 

 those magnetic changes which are due to the action of the Sun, 

 and which are brought about by means of the ether which 

 brings to us his radiant heat and light. In his discussion of 

 the magnetic effects observed on the earth's surface. General 

 Sabine has shown the existence of diurnal variations due to the 

 magnetic action of the sun ; also the magnetic disturbances, 

 aurora and earth-currents, which are now again beginning to 

 be large and frequent, have been set down to disturbances in 

 the sun. 



Although iron, when raised to incandescence, has its power of 

 attracting a magnet very greatly diminished, we have no proof 

 that it has absolutely no magnetic 1 ower left, and with a slight 

 magnetic action the quantity of iron in the sun would be suffi- 

 cient to account for the diurnal variations of the magnetic 

 needle. During the last few weeks I have been engaged in 

 examining the declinatioii curves for the month of March, 1879, 

 which have been kindly lent to the Kew Committee by the 

 directors of the Observatories of St. Petersburg, Vienna, Lis- 

 bon, Coimbra, and Stonyhurst. Other curves are on their way 

 from more distant stations, but have not yet been examined. 

 (jn comparing them with the Kew curves for the same period, I 

 find the most remarkable coincidences between the curves from 

 these widely-distant stations. It was previously known that 

 there was a similarity between disturbances at different stations, 

 and in one or two cases a comparison between Lisbon and Kew 

 had been made many years ago by Seiior Capello and Prof. 

 Balfour Stewart, but the actual photographic magnetic records 

 from several stations have never been previously collected, and 

 so the opportunity for such comparisons had not arisen. Allow 

 me to draw attention to a few of the more prominent features 

 of these comparisons which I have made. On placing the 

 declination curves over one another, I find that in many cases 

 there is absolute agreement between them, so that the rate of 

 change of magnetic disturbances at widely-distant stations like 

 Kew, Vienna, and St. Petersburg, is precisely the same ; also 

 similar disturbances take place at different stations at the same 

 absolute time. It may be s'ated generally, for large as well as 

 small disturbances, that the east and west deflections of the 

 declination needle take place at the same time and are of the 

 same character at these widely-distant stations. 



There are exceptions to this law. Some disturbances occur at 

 one or two stations and are not perceived at another station. 

 Many instances occur, where, up to a certain point of time, the 

 disturbances at all the stations are precisely alike, but suddenly 

 at one or two stations the disturbance changes its character : for 

 instance, on comparing Kew and St. Petersburg, we get perfect 

 similarity followed by deflections of the needle opposite ways at 

 the same instant, and in some such cases the maxima in opposite 

 directions are reached at the same instant, showing that the 

 opposite deflections are produced by the same cause, and that 

 the immediate cause or medium of disturbance in such a case is 

 not far olf ; probably it is some change of direction or intensity 

 of the earth's magnetism arising from solar action upon it. 



Generally, after an hour or two, these differences in the effects 

 of the disturbance vanish, and the disturbances again become 

 alike and simultaneous. In such cases of difference, if the curve 

 tracing of the horizontal or the vertical force be examined, it is 

 generally found that, at the very same instant of absolute time, 

 with the beginning of these opposite movements there w.as an 

 increase or a diminution in the horizontal force, and that the 

 horizontal force continues to change as long as there is any dif- 

 ference in the character of the declination curves. It is clear 

 then from these effects that the cause or causes of magnetic dis- 

 turbances are in general far distant from the earth's surface, even 

 when those disturbances are large; but that not unfrequently these 

 cau-es act on magnetic matter nearer to the surface of the earth, 

 and therefore at times between two places of observation, and 

 nearer to one than another, thus producing opposite effects on the 

 declination needle at those places; in such cases the differences are 

 probably due to changes in the earth's magnetic force. Now, 



