April /a,, 1889J 



NATURE 



537 



In conclusion, it appears to me that the close relationship of 

 the metals aluminium, gallium, indium, iron, and chromium, 

 makes it probable that molecules of both formulae M^Rg and 

 MR3 may be capable of existence in the case of all these metals, 

 even though the conditions necessary for the stability of the 

 higher molecules have not yet been attained for indium and 

 chromium chlorides. That the conditions have been attained in 

 the case of the chlorides of aluminium, gallium, and iron, 

 appears to me to admit of no doubt. SYDNEY YouNG. 



University College, Bristol, March 23. 



Luminous Night-Clouds. 



In accordance with my anticipations (see Astr. Nachr., 2885), 

 luminous night-clouds have now been seen at the southern point 

 of South America. Herr Stubenrauch, meteorological observer 

 at Punta-Arenas, writes to me that he twice saw the phenomenon 

 in December 1888. According to the same observer, it was 

 noticed several years ago by a naval officer in the Beagle 

 Channel, rather to the south of Punta-Arenas. The description 

 given by Herr Stubenrauch leaves no room for doubt that the 

 phenomenon is identical with that observed in Europe. 



Sternwarte, Berlin, March 28. O. Jesse. 



Zodiacal Light Observations. 

 Could any of your readers furnish me with a list of observa- 

 tions of zodiacal light, or refer me to any record where such a 

 list can be found ? I applied to the Meteorological Office some 

 years ago, and found that no such list was to be obtained. All 

 I require is the precise time of the display, the place of observa- 

 tion, and any other mathematical observations concerning the 

 angle of inclination, &c., which may be relied on. 



W. DONISTHORPE. 



32 Pembridge Villas, W., March 30. 



Vapour, or Meteoritic Particle. 



About 6.30 p.m. on Friday last, while out in the country, I 

 observed a large meteor falling slowly and almost vertically in 

 the north-north-east. After it had disappeared, half-way between 

 the zenith and the horizon, I noticed, in the strong twilight, a 

 faint phosphorescent trail, which did not disappear, but changed 

 to a straw-colour, like a streak of vapour illuminated by the 

 setting sun. Gradually the shaft expanded in the centre and 

 contracted at the ends, until it assumed the shape of a balloon. 

 Continuing to change, it flattened out horizontally like a foot- 

 ball, and apparently about half the size ; and it looked a little 

 brighter as it became more condensed. This process occupied 

 •quite half an hour, and the object remained like a nebulous 

 patch lit up by the sun's rays, until that orb was well below the 

 horizon, finally disappearing about 7.15 p.m. That part of the 

 sky was perfectly clear— there were no clouds except the usual 

 dense bank on the horizon. F. B. 



Rugby, March 27. 



The Satellite of Procyon. 



With reference to Mr. Barr's letter on p. 510, I would men- 

 tion that Mr. Burnham has lately observed Procyon with the 

 36-inch refractor at the Lick Observatory, and finds no trace of 

 any close companion with powers up to 3300. H. Sadler. 



March 29. 



RECENT RESEARCHES ON THE RARE 

 EARTHS AS INTERPRETED BY THE 

 SPECTROSCOPE} 

 TF I name the spectroscope as the most important scien- 

 -*• tific invention of the latter half of this century, I shall 

 not fear to be accused of exaggeration. Photography has 

 rendered vast services in recording astronomical and bio- 

 logical phenomena, and it even supplies us with indirect 

 means of studying ray vibrations to which the human 

 retina does not respond. The electro-acoustic devices of 



Abstract of .Address deliv>^red on Thursday, March a8. at the annual 

 eral meeting of the Chemical Societ 

 .R.S. 



general meeting of the Chemical Society, by the President, Mr. W. Crookes, 



Edison and his co-workers permit almost magical com- 

 munication between human beings. Ruhmkorff's coil 

 and the Geissler tube have rendered notable service in 

 physical investigations ; and the electric lamp promises 

 to aid in exploring the internal parts of living animals as 

 well as in studying the organic forms of the deep sea. 

 But in the spectroscope we possess a power that enables 

 us to peer into the very heart of Nature. In the extent 

 of its grasp and the varied character of its applicability it 

 surpasses the telescope, and at least rivals the micro- 

 scope. It enables the astronomer to defy immeasurable 

 distance, and to study the physical condition and the 

 chemical composition of the sun and the stars as if they 

 were within touch, and even to ascertain the direction of 

 their movements. 



Without attempting to discuss the import of the results 

 thus gained — which would lead us too far — I may point 

 out that they overthrow a dogma concerning the classifica- 

 tion of the sciences. It has been said that the simpler and 

 more general sciences lend both doctrines and methods to 

 the more complex and less general sciences, and that the 

 latter give nothing in return. But we now see chemistry 

 endowing astronomy with an original and fruitful method 

 of research. 



Turning to the very opposite extremity of the scien- 

 tific hierarchy, we find that to the biologist the spectro- 

 scope is of value in studying the relations of animal and 

 vegetable fluids, and even of certain tissues. But this 

 wonderful instrument is clearly destined to play its chief 

 part in what is called terrestrial chemistry — the field 

 where it has won the most signal triumphs. 



It must be remarked, despite this vast range of 

 applicability — a range sweeping through the whole uni- 

 verse and embracing all the four elements of antiquity — 

 and despite the astonishing results already achieved and 

 the prospect of greater revelations to come, that the 

 spectroscope is still inadequately appreciated by professed 

 men of science, and in consequence is to a great extent 

 ignored by the " educated and intelligent public." In 

 urging its more thorough recognition, I do not advocate 

 the formation of Spectroscopic Societies for the frag- 

 mentary study of everything that can be observed with a 

 spectroscope. But I recommend researching chemists 

 to appeal to this instrument wherever requisite and 

 possible. 



An elaborate spectroscopic study of the basic con- 

 stituents of rare minerals from different localities would 

 be of great value, and I would suggest that on all possible 

 occasions meteorites should be submitted to careful 

 spectroscopic analysis. 



I do not propose to discuss all the splendid achieve- 

 ments of the spectroscope in chemistry ; nor its applica- 

 tions in ordinary analysis, qualitative and quantitative ; 

 nor the conduct of technical operations, such as the 

 Bessemer process. I confine myself to the light thrown 

 by the spectroscope upon the nature and the relations of 

 our elements, real or supposed. 



Though systematically employed by few experiment- 

 alists, the spectroscope has already led to the discovery 

 of several hitherto unknown elements. In the early days 

 of spectrum analysis, attention was mainly concentrated 

 on the flame spectra : that is, the bodies in question were 

 vaporized and rendered luminous by the action of a flame, 

 such as that of the Bunsen burner or of the o.xyhydrogen 

 jet. This procedure in the hands of Bunsen and Kirch- 

 hoffgave us caesium and rubidium; afterwards, in my 

 own hands, thallium ; and in those of Reich and Richter, 

 indium. 



Then followed the production and examination of spark 

 spectra. The spark produced by means of the induction 

 coil, especially when its energy is reinforced by the inter- 

 calation of a Leydfen jar, volatilizes and renders luminous 

 minute portions of matter, solid, liquid, or gaseous, which 

 may then be examined by the spectroscope. In this 



