IQO 



NATURE 



[December 20, 1900 



was examined end on, so that the radiation probably included 

 rays emitted from the neighbourhood of the negative pole. The 

 whole of the hydrogen had been removed from the Bath gas, but 

 not all the argon. In the spectrum of this gas the rays of 

 helium are dominant, decidedly stronger than those of neon, 

 although the latter are very bright. In the spectrum of the 

 residue of atmospheric air the proportion of helium to neon 

 seems reversed, for in this the yellow neon line is as much more 

 brilliant than the yellow helium line as the latter is the more 

 brilliant in the spectrum of Bath gas. All the prominent lines 

 in the spectrum of the volatile residue of Bath gas were also in 

 that of the residue of atmospheric air except the argon lines. 

 There were, on the other hand, many lines in the latter not 

 traceable in the former, some of them rather conspicuous, such 

 as the ray at about A. 4664. It is, of course, probable that such 

 rays are the outcome of some material not contained in the Bath 

 gas. A very conspicuous pair of lines appears in photographs 

 of the spectrum of the air residue, at about A 3587, which is not 

 traceable in the spectrum of Bath gas. The helium line, 

 ^ 35^7 '4> is seen in the latter spectrum, but is quite obscured in 

 the former spectrum by the great intensity of the new pair. 

 This helium ray is really a close double, with the less refrangible 

 component much the weaker of the two, but the new pair are 

 wider apart, and of nearly equal intensities ; this character also 

 distinguishes them from the strong argon line at \ 3588 '6. 

 They are, however, very much more intense at the negative 

 pole than in the capillary, and it will require a good deal more 

 study to determine whether these rays, and many others which 

 we have not tabulated, are due to the peculiarity of the stimulus 

 at the negative pole or to the presence of a previously 

 unrecognised material. 



As our mixture of gases probably includes some of all such 

 gases as pervade interplanetary and interstellar space, we early 

 looked in their spectra for the prominent nebular, coronal and 

 auroral rays. Searching the spectrum about A 5007 no indica- 

 tion of any ray of about that wave-length was visible in the 

 spectrum of any one of the three tubes which had been filled as 

 above described. Turning to the other green nebular line at 

 about A 4959 we found a weak rather diffuse line to which our 

 first measure assigned a wave-length 495S. The correctness of 

 this wave-length was subsequently verified by measuring with a 

 micrometer eye-piece the distances of the line from the helium 

 lines A4922'i and A 50157 which were in the field of view at 

 the same time. The position of the line was almost identical 

 with that of the iron spark line A 4957 '8, and the conclusion 

 arrived at was that the wave-length was a little less than 4958, 

 and that it could not be the nebular line. There remained the 

 ultra-violet line A 3727. Our photographs showed a rather strong 

 line very close to the iron spark line A 3727 -8, but slightly more re- 

 frangible. As the line is a tolerably strong one it could be photo- 

 graphed with a grating spectrograph along with the iron lines. 

 This was done, and the wave-length deduced from measuring 

 the photograph was 3727*4. This is too large by an amount 

 which considerably exceeds the probable errors of observation, 

 and we are forced to conclude that the nebular material is either 

 absent from our tubes, or does not show itself under the treat- 

 ment to which it has been subjected. 



Although the residual gases of the atmosphere, uncondensed 

 at the temperature of liquid hydrogen, do not show the nebular 

 lines, we found that another tube gave a ray very close indeed to 

 the principal green nebular ray. This tube had been filled with 

 gas prepared in the same way as the others, with the exception 

 that, in passing from the vessel into which the first fraction of 

 liquid air was distilled, it was not passed through a U-tube im- 

 mersed in liquid hydrogen on its way to the exhausted tube. In 

 consequence it contained traces of nitrogen and argon, and 

 when sparked showed the spectra of these elements as well as 

 those of hydrogen, helium, &c. The nitrogen spectrum dis- 

 appeared after some sparking, but the tube still showed rays of 

 argon as well as those of the gases in the other tubes. On ex- 

 amining the spectrum of the negative pole in the neighbourhood 

 of the principal nebular green ray, a weak ray was seen in 

 additioii to those given by the other tubes. It was found by 

 comparison with the nitrogen rays A 50027 and A 50057 to be 

 a little less refrangible than the latter of these rays, and by 

 measuring its distance from the nitrogen rays and from the, two 

 helium rays A 4922-1 and A 50157 with a micrometer eye-piece, 

 the wave-length A 50077 for the new ray was deduced. This 

 looks as if we might find the substance which is luminous in 



NO. 1625, VOL. 63] 



nebulae to be really present in the earth's atmosphere, and we 

 hope shortly to be able to verify the observation of it. 



Turning to the coronal rays, our tubes emit a weak ray at 

 about A 5304. This is not far from the wave-length A 53037 

 assigned by Sir N. Lockyer to the green coronal ray. It is, 

 however, greater than that assigned by Campbell, namely, 

 5303 '26. Other lines observed by us near the places of coronal 

 lines are at wave-lengths about 4687, 4570, 4358, 4323, 4232, 

 4220, 3985, 3800. These are all weak lines except that at 

 A 4232, which is of tolerable strength, and that at A 4220, which 

 is rather a strong line. The wave-lengths 4323, 4232, 4220 and 

 3800 come very close to those assigned to coronal rays, but the 

 others hardly come within the limits of probable error. The 

 ray 4220 seems too strong in proportion to the others, but the 

 strength of that at 4232 seems to accord with the strength of the 

 corresponding ray in the corona. It will be seen that the rays 

 we enumerate above correspond approximately to the stronger 

 rays in Sir N. Lockyer's list. Further measures of the wave- 

 lengths of the faint lines are needed before we can say definitely 

 whether or no we have in our tubes a substance producing the 

 coronal rays, or some of them. 



As to the auroral rays, we have not seen any ray in the 

 spectrum of our tubes near A 5571*5, the green auroral ray. We 

 have observed two weak rays at A 4206 and A 4198, which may 

 possibly, one or both, represent the auroral ray A 420. The very 

 strong ray of argon, A 4200*8, would make it probable that argon 

 was the origin of this auroral ray, if the other, equally strong, 

 argon rays in the same region of the spectrum were not absent 

 from the aurora. Nor have we found in the spectrum of our 

 tubes any line with the wave-length 3915, which is that of 

 another strong auroral line. On the other hand it seems pro- 

 bable that the strong auroral line A 358 may be due to the 

 material which gives us the very remarkable pair of lines at 

 about the place of N of the solar spectrum, A 3587, which are very 

 strong in the spectrum of the negative pole, but only faint in that 

 of the capillary part of our tubes. It may well be that the auroral 

 discharge is analogous to that about the negative pole. We have 

 also a fairly strong ray at A 3700, which may be compared to the 

 remaining strong ray observed in the aurora A 3700. This, how- 

 ever, is a ray which is emitted from the capillary part of our 

 tubes as well as from the negative pole, and is, moreover, 

 emitted by Bath gas, and may very likely be a neon ray. 



We hope to pursue the investigation of this interesting spec- 

 trum, and if possible to sort out the rays which may be ascribed 

 to substances such as neon and those which are due to one or 

 more other substances. The gas from Bath, even if primarily 

 derived from the atmosphere — which is by no means sure — 

 seems to have undergone some sifting which has affected the 

 relative proportions of helium and neon, and a more thorough 

 comparison of its spectrum with that of the residual atmospheric 

 gases may probably lead to some disentanglement of the rays 

 which originate from different materials. The arrangement of 

 the rays in series, if that could be done, would be a step in the 

 same direction. 



The table appended to the above paper is not given here, but 

 it consists chiefly of wave-lengths expressed in four figures only. 



THE TREA TMENT OF LONDON SE WA GE.^ 



Y^HEN, some years since, the raw sewage of London was 

 regularly poured into the river in the neighbourhood of 

 the city, the road detritus and putrescible faecal matter which 

 were delivered in the sewage settled on the river bed and fore- 

 shores. The road detritus tended to permanently reduce the 

 depth of the river ; while the putrescible matter, arriving faster 

 than it could be removed by the river or could be destroyed by 

 inoffensive bacterial action, accumulated as a deposit on the fore- 

 shores and floated in masses of thick scum on the river. It 

 there underwent foul putrefactive changes, rendering the river 

 most offensive to those who navigated it or lived and worked 

 near its banks, and almost intolerable in summer weather, even 

 to those who crossed its bridges. That this result was inevitable 

 will be understood when it is remembered that the sewage con- 

 sists of the whole of the water-supply and rainfall over the 



1 Abridged from a paper read before the Society of Arts, on December 

 12, by Prof. Frank Clowes. 



