262 



NATURE 



\_7uly 2 1, 1 88 1 



bright parts having the aspect of short lines, not occupying 

 the whole width of the spectrum. This was perhaps 

 merely a result of fatigue of the eyes ; these phenomena 

 were only produced during the first two nights. 



" It appeared to me important to follow the modifica- 

 tions the spectrum might undergo as the comet went away 

 frim the sun. These modifications were produced with 

 perfect distinctness. In the spectrum of the nucleus the 

 violet radiations were extinguished first. About June 30 

 the most refrangible part, commencing with the green 

 band (X = 516), had sensibly lost its brightness and 

 became invisible in the region G, while the yellow and 

 red appeared to me as bright as on the first day. The 

 bands, masked at first by the brightness of the con- 

 tinuous spectrum, became each day more visible in the 

 neighbourhood of the nucleus, and during the night of 

 July I they were perfectly distinguished on the nucleus 

 itself. 



" The measurements successively made of the bands of 

 the comet and of those of the alcohol flame led me to 

 conclude the identity of the two spectra. The green band 

 however, the most brilliant, seemed a little more refracted 

 in the comet than in the flame. To submit this matter to 

 a decisive te^t, a total reflection-prism was adjusted on 

 the slit so as to cover half of it. On placing the two 

 spectra together I observed that they were strikingly 

 similar when they had the same brightness, but that the 

 green band appeared indeed more refracted in the comet 

 when the spectrum of the flame was more brilliant. The 

 comparison made directly between the two spectra, and 

 the perfect coincidence of the bands, dispense with the 

 necessity of giving numbers furnished by my micrometric 

 measurements. They would not add anything to the 

 certainty of the result. 



"As to the violet band, it has not been possible for me 

 to see it in a certain manner, even using a very small 

 dispersion and a very small ocular enlargement. There 

 is not in this fact anything surprising, if we take account 

 of atmospheric absorption and of variations of brightness ^ 

 undergone by the violet band, when the experimental 

 conditions are varied. We know that in the ordinary 

 flame of alcohol it is very brilliant ; but if this flame be 

 cooled by means of several folds of metallic sheeting, it 

 becomes very weak and tends to disappear, while the 

 other bands sensibly retain their habitual aspect. 



" Continuing my observations till the present, I have 

 found the continuous spectrum of the nucleus diminish 

 progressively in brightness and extent, especially on the 

 violet side. At present it has the aspect of a thin lumi- 

 nous thread, hardly passing beyond the line F. The 

 bands, on the other hand, seem to have retained their 

 intensity in the head of the comet. In the tail, and to a 

 distance from the nucleus equal to twice or thrice the 

 diameter of the head, they are still seen, but very faintly. 

 Further on one sees only a continuous spectrum due 

 perhaps to the light of the moon dift'used by the haze, 

 pretty thick during the last nights of observation. 



" It seems to result from this that the cometary mass is 

 formed in part of an incandescent gas, characterised by 

 the spectrum of bands, and in part of solid or liquid 

 matter, likewise incandescent, but in a state of extreme 

 division, emitting a white light which belongs to it, and 

 capable of reflecting in a certain proportion the liglit it 

 receives from the sun. All the spectroscopic observa- 

 tions hitherto made on comets indicate the existence of 

 carbon in the gases producing the band-spectrum Dr. 

 Huggins has given this conclusion a striking demon- 

 stration by showing, with photography, the existence of 

 two bands of carbon in the ultra-violet spectrum of the 

 comet. 



" I have the honour to submit to the Academy three 

 drawings representing (i) the spectrum of the alcohol 

 flame, (2) the spectrum of the comet during the night of 

 June 24, and (3) the same spectrum on July i." 



WIDTH OF MR. RUTHERFURiyS RULINGS 



T) Y the direction of C. P. Patterson, the Superintendent 

 -'-' of the U.S. Coast and Geodetic Survey, I have long 

 been engaged in the precise measurement of a wave- 

 length of light, in order to obtain a check upon the secular 

 molecular changes of metallic bars used as standards ot 

 length. In advance of the publication of this work it 

 may be useful to say I have found that the closest-ruled 

 diffraction-plates by Mr. Lewis Rutherfurd have a mean 

 width of ruling which varies in different specimens from 

 68078 to 6S0S2 lines to the decimetre, at yo'' F. There is 

 a solar spectral line, well suited for precise observation, 

 whose minimum deviation with one of Mr. Rutherfurd' s 

 plates in the spectrum of the second order with the closest 

 ruled plates is 45" 01' 56" at 70'' F. I would propose that 

 this line be adopted as a standard of reference by such 

 observers of wave-lengths as desire to escape the arduous 

 operation of measuring the mean width of their rulings; 

 for by means of the measures which are shortly to be 

 published it will be possible to deduce from the minimum 

 deviation of this line produced by any given gitter, the 

 me in width of that gitter, and consequently the wave- 

 length of any other line whose deviation has been observed 

 with it. The accuracy of this method will greatly exceed 

 that of assum'ng Angstrom's measures to be correct. The 

 wave-length of the line in question (still subject to some 

 corrections which may be considerable) is 5624825. 

 Angstrom gives 562336. C. S. Peirce 



CITY AND GUILDS OF LONDON INSTITUTE 



T T would seem as if at last, after long years of waiting, 

 •'- there were some hope that the views which for the 

 last quarter of a century have been so persistently advo- 

 cated touching technical education, ware about to bring 

 forth more fruit in London. 



In season and out of season, since the note was first 

 sounded by the late Prince Consort, one far-seeing advo- 

 cate after another, and among these we must specially 

 name Mr. Samuelson, Mr. Mundella, and Sir Henry Cole, 

 have cried in the wilderness touching the need of more 

 scientific instruction. At last it does seem as if there is 

 an awakening, as if a part of the idea was realised in the 

 Institute, the foundation-stone of which was laid at South 

 Kensington on Monday by the Prince of Wales. No 

 doubt in the building which has been begun a national 

 school of science, theoretical and applied, worthy of a 

 country like ours, may grow up. Mr. Mundella will 

 rejoice that at last he has an opportunity of carrying 

 out with something like adequacy the views on education 

 of which he has been so long a strenuous advocate. We 

 hope next week to give a detailed description and illustra- 

 tion of the new building ; and meanwhile will content 

 ourselves with briefly referring to what took place on 

 Monday. 



The company present to receive the Prince of Wales 

 was large and distinguished, including many eminent 

 men of science. The Lord Chancellor, as Chairman of 

 the Institute, addressed the Prince, expressing the gratifi- 

 cation of the Council that His Royal Highness had 

 consented to become president. The Lord Chancellor 

 then traced the growth of the Institute and the eflbrts of 

 the City Guilds to improve the technical education of the 

 country. 



"Since July of last year," the Lord Chancellor said, 

 "the date of the incorporation of the Institute, its 

 work has satisfactorily increased, and the Council have 

 a lively and grateful recollection of the assistance and 

 encouragement afforded to them by His Royal Highness, 

 Prince Leopold, Duke of Albany, who in May last laid 

 the foundation-stone of the Finsbury Technical College, 

 a college that has been established by this Institute, and 



