Sept. 30, 18S0] 



NA rURE 



shall have to give an account of some changes which have not 

 found a place under the previous heads." 



Space will only permit us to quote a few of the questions 

 raised. It is now generally admitted that pressure is the prin- 

 cipal cause which determines the widening of lines, but it is not 

 generally know-n that a different appearance of the lines may be 

 presented according as the pressure is due to the impact of 

 similar or dissimilar molecules ; thus a molecule of sodium will 

 widen its lines more easily in an atmosphere of sodium than in 

 another atmosphere. Mr. Lockyer has observed that the lines 

 of oxygen or nitrogen may be obtained sharp at atmospheric 

 pressure by mixing a small quantity of one gas with the other. 

 The gas which is present in small quantities has its lines sharp. 



The curious fact is mentioned that when a line widens un- 

 symmetrically it widens in nearly all cases more towards the red, 

 and then towards the violet end. 



In that part of the report which relates to multiple spectra an 

 account is given- of the gradual spreading of the opinion that 

 these spectra are due to ditTerent molecular groupings. The 

 question of long and short lines is next discussed, and great stress 

 is laid on the fact that the longest lines are by no means always 

 the strongest. An abstract of Mr. Lockyer's work on the sub- 

 ject is given, and of the confirmation which his results have found 

 in later work. Thus Mr. Lockyer found that the longest lines 

 were always the first to be reversed. Professors Liveing and 

 Dewar have since examined the absorption-spectra of many me- 

 tallic vapours. The lines which they have seen reversed were 

 nearly in all cases those w hicli are longest in the spark, though 

 not always those which are strongest. Results obtained by M. 

 Lecoq de Boisbaudran with sparks, the temperature of which was 

 lower than in the ordinary jar-discharge, also confirm Mr. 

 Lockyer's results. Discussing the attempts which have been 

 made to explain these and other facts, it is again mentioned 

 that we must assume the impacts of a similar molecule to pro- 

 duce a greater effect than ihe impacts of a dissimilar one. The 

 last part of the report treats of some other changes in the relative 

 intensities of lines. We only mention the experiments in which 

 Mr. Lockyer found sometimes the green sodium line to be 

 present without the well-known yellow double line. The report 

 concludes as follows : — 



" We have here again two hypotheses, that of molecular shocks 

 and that of molecular combinations. Both explain the facts satis- 

 factorily, and I do not think that one of them necessarily excludes 

 the other. I believe, on the contrary, that a line can be drawn, 

 and that while the regular changes observed chiefly in band- 

 spectra may be due to one cause, the often irregular changes in 

 metallic spectra, where one set of lines disappears and another 

 appears often on the violet side, but sometimes towards the red, 

 may be due to another cause. 



" It is often said that we must not ascribe the same phenomenon 

 to two different causes, when one of them is sufficient to explain 

 it; but the point at issue is whether the phenomena are the 

 same in all cases. An advance of science has c instantly led to 

 the separation of phenomena which were formerly considered to 

 be connected together, and we believe that the further develop- 

 ment of the different points we have attempted to discuss, in 

 which different observers have strongly taken up opposite 

 opinions, will lead to tie blending together of different views 

 rather than the entire elimination of one of them." 



Prof. Hartley, in his part of the report, gives us an account of 

 our knowledge on emission spectra in the ultra-violet region. 

 He treats especially of the researches on the solar spectrum by 

 Mascart, Draper, and Cornu. 



Prof. A. K. Huntington reports on the absorption spectra in 

 the ultra-violet region. The results obtained by Prof. Stokes 

 and Dr. Miller are given in detail. Amongst the results 

 obtained by Dr. Miller, it seems especially interesting to notice 

 the connection which apparently exists between the absorbing 

 properties of a liquid and that of its vapour. When one of 

 them is transparent to the ultra-violet rays the other is also, and 

 vice z'tTsd. 



Prof. Soret, it is well known, constructed a few years ago a 

 spectroscope with a fluorescent eyepiece, and has by means of it 

 carried researches in the ultra-violet p .rts of the spectrum. We 

 notice especially the examination of absorption-spectra of the 

 bases of gadolinite, and the conclusions drawn from it on the 

 existence of new elementary bodies. Prof. Cornu has given 

 much attention to the absorption power of our atmosphere, and 

 we find a full account of his experiments in Prof. Huntington's 

 report. In conclusion we have a short abstract of the work 



done by Professors Hartley and Huntington on absorption- 

 spectra in the ultra-violet region. They obtained the following 

 results : — 



1. The normal alcohols of the series C4H2„_iOH are remark- 

 able for transparency to the ultra-violet rays of the spectrum, 

 pure methylic alcohol being nearly as much so as water. 



2. The normal fatty acids exhibit a greater absorption of the 

 more refrangible rays of the ultra-violet spectrum than the 

 normal alcohols containing the same number of carbon atoms. 



3. There is an increased absorption of the more refrangible 

 rays corresponding to each increment of CH„ in the molecule of 

 the alcohols and acids. 



4. Like tlie alcohols and acids, the ethereal salts derived from 

 them are highly transparent to the ultra-violet rays, and do not 

 exhibit absorption-bands. 



Interesting results were also obtained by the examination of 

 substances containing the benzene nucleus, and in a separate 

 paper the absorption-spectra of essential oils were examined and 

 discussed. Prof. Hartley has still further extended the researches 

 jointly begun with Prof. Huntington, and has arrived at the con- 

 clusion that no molecular arrangement of carbon atoms causes 

 selective absorption, unless three pairs are doubly linked together 

 in a closed chain. 



It will be seen that a few only of the branches of spectrum 

 analysis have been discussed in the present report, and next year 

 no doubt will bring us a further instalment of a work which we 

 hope will prove useful to those who are interested in spectro- 

 scopic investigations. 



A CRICUL TURA L C HEM 1ST R V ' 

 IIL 

 T HAVE thus far directed attention to some points of importance 

 in connection with the sources of the constituents of our crops, 

 and I must now briefly refer to some in connection with the 

 composition, and to some relating to the uses, of the crops 

 themselves. 



As to composition, I must confine myself to indicating 

 something of what is known of the condition of the nitrogen in 

 our various crops ; though I had intended to say something 

 respecting the carbohydrates, and especially respecting the 

 various members of the cellulose group. 



As to the nitrogen — in our first experiments on the feeding of 

 animals, made in 1S47, 1S4S, and 1849, the results of which 

 were published in the last-mentioned year — we found that, in the 

 case of succulent roots used as food, not only were they not of 

 value as food in proportion to their richness in nitrogen, but 

 when the percentage of it was higher than a certain normal 

 amount, indicating relative succulence and immaturity, they were 

 positively injurious to the animals. So marked was the variation 

 of result according to the condition of maturity or otherwise of 

 of the foods employed, that, when reviewing the results of the 

 experiments which had up to that time been conducted, in a 

 paper read before this Section of the British Association at the 

 Belfast meeting in 1S52 (and which was published in full in the 

 annual volume'), we stated that the mode of estimating the 

 amount of proteine compounds by multiiilying the percentage of 

 nitrogen by 6'3 was far from accurate, especially when applied 

 to succulent vegetable foods, and that the individual compounds 

 ought to be determined. The Rothamsted laboratory staff was 

 however much smaller then than it is now, and with the pressure of 

 many other subjects upon us, it was at that time quite impossible 

 to follow up the inquiry in that direction. 



It is indeed only witliin the last ten years or so that the ques- 

 tion has been taken up at all systematically ; but we are already 

 indebted to E. Schulze, A. Urick, Church, Sachsse, Maercker, 

 Kellner, Vines, Emmerling, and others, for important results 

 relating to it. 



Our'knowledge in regard to the subject is however still very 

 imperfect. But it is in progress of investigation from two dis- 

 tinctly different points of view — from that of the vegetable 

 physiologist and that of the agricultural chemist. The vegetable 

 physiologist seeks to trace the changes that occur in the ger- 

 mination of the seed, and during the subsequent life-history of 

 the plant, to the production of seed again. The agricultural 



' Opcnin" Address in Section B (Chemical Science), at the Swansea 

 meeting of" the British Association, by J. H. Gilbert, Ph.D., F.R.S., 

 V B C S., F.L.S.. President of the Section. Continued from p. 499. 



'= "On the Composition of Foods •" — l-:— •" l,>-.-„.ro„„„ on 

 Feeding of Animals." 



elation to Respir 



nd the 



