214 



SCIENCE. 



Vol.. XVIll. No. 454 



proportion to give a spectrum. Lemstrom, indeed, states that 

 he saw this line in the silent discharge of a Holtz machine 

 on a mountain in Lapland. The lines may not have been 

 obtained in our laboratories from the atmospheric gases on 

 account of the difficulty of reproducing in tubes with suffi- 

 cient nearness the conditions under which the auroral dis- 

 charges take place. 



In the spectra of comets the spectroscope has shown the 

 presence of carbon presumably in combination with hydro- 

 gen, and also sometimes with nitrogen; and in the case of 

 comets approaching very near the sun, the lines of sodium, 

 and other lines which have been supposed to belong to iron. 

 Though the researches of Professor H. A. Newton snd of 

 Professor Schiaparelli leave no doubt of the close connection 

 of comets with corresponding periodic meteor-swarms, and 

 therefore of the probable identity of cometary matter with 

 that of meteorites, with which the spectroscopic evidence 

 ■agrees, it would be perhaps unwise at present to attempt to 

 define too precisely the exact condition of the matter which 

 forms the nucleus of the comet. In any case the part of the 

 liglit of the comet which is not reflected solar light can 

 scarcely be attributed to a high temperature produced by the 

 clashing of separate meteoric stones set up within the nucleus 

 by the sun's disturbing force. We must look rather to dis- 

 ruptive electric discharges, produced probably by processes 

 of evaporation due to increased solar heat, which would be 

 amply sufficient to set free portions of the occluded gases into 

 the vacuum of space. May it be that these discharges are 

 assisted, and indeed possibly increased, by the recently dis- 

 covered action of the ultra-violet part of the ,sun's light ? 

 Lenard and Wolfe have shown that ultra violet light can 

 produce a discharge from a negatively electrified piece of 

 metal, while Hallwachs and Righi have shown further that 

 ultra-violet light can even charge positively an unelectrifled 

 piece of metal. Similar actions on cometary matter, un- 

 screened as it is by an absorptive atmosphere, at least of any 

 noticeable extent, may well be powerful when a comet ap- 

 proaches the sun, and help to explain an electrified condition 

 of the evaporated matter which would possibly bring it un- 

 der the sun's repulsive action. We shall have to return to 

 this point in speaking of the solar corona. 



A very great advance has been made in our knowledge of 

 the constitution of the sun by the recent work at the Johns 

 Hopkins University by means of photography and concave 

 gratings, in comparing the solar spectrum, under great re- 

 solving power, directly with the spectra of the terrestrial 

 elements. Professor Rowland has shown that the lines of 

 thirty-six terrestrial elements at least are certainly present in 

 the solar spectrum, while eight others are doubtful. Fifteen 

 elements, including nitrogen as it shows itself under an elec- 

 tric discharge in a vacuum tube, have not been found in 

 the solar spectrum. Some ten other elements, inclusive 

 of oxygen, have not yet been compared with the sun's spec- 

 trum. 



Rowland remarks that of the fifteen elements named as 

 not found in the sun, many are so classed because they have 

 few strong lines, or none at all, in the limit of the solar 

 spectrum as compared by him with the arc. Boron has only 

 two strong lines. The lines of bismuth are compound and 

 too diffuse. Therefore even in the case of these fifteen ele- 

 ments there is little evidence that they are really absent from 

 the sun. 



It follows that if the whole earth were heated to the tem- 

 perature of the sun, its spectrum would resemble very closely 

 tlic solar spectrum. 



Rowlandlias not found any lines common to several ele- 

 ments, and in the case of some accidental coincidences, more 

 accurate investigation reveals some slight difference of wave- 

 length or a common impurity. Further, the relative strength 

 of the lines in the solar spectrum is generally, with a few 

 exceptions, the same as that in the electric arc, so that Row- 

 land considers that his experiments show "very little evi- 

 dence" of the breaking up of the terrestrial elements in the 

 sun. 



Stas, in a recent paper, gives the final results of eleven 

 years of research on the chemical elements in a state of 

 purity, and on the possibility of decomposing them by the 

 physical and chemical forces at our disposal. His experi- 

 ments on calcium, strontium, lithium, magnesium, silver, 

 sodium, and thallium show that these substances retain their 

 individuality under all conditions, and are unalterable by 

 any forces that we can bring to bear upon them. 



Profess;)r Rowland looks to the solar lines which are un- 

 accounted for as a means of enabling him to discover such 

 new terrestrial elements as still lurk in rare minerals and 

 earths, by confronting their spectra directly with that of the 

 sun. He has already resolved yttrium spectroscopically 

 into three components, and actually into two. The compari- 

 son of the results of this independent analytical method with 

 the remarkable but different conclusions to which M. Lecoq 

 de Boisbaudran and Mr. Crookes have been led respectively, 

 from spectroscopic observation of these bodies when glowing 

 under molecular bombardment in a vacuum tube, vrill be 

 awaited with much interest. Ills worthy of remark that, as 

 our knowledere of the spectrum of hydrogen in its complete 

 form came to us from the stars, it is now from the sun that 

 chemistry is probably about to be enriched by the discovery 

 of new elements. 



In a discussion of the Bakerian lecture for 1885 of what we 

 knew up to that time of the sun's corona, I was led to the 

 conclusion that the corona is essentially a phenomenon simi- 

 lar in the cause of its formation to the tails of comets — 

 namely, that it consists for the most part probably of matter 

 going from the sun under the action of a force, possibly 

 electrical, which varies as the surface, and can therefore in 

 the case of highly attenuated matter easily master the force 

 of gravity even near the sun. Though many of the coronal 

 particles may return to the sun, those which form the long 

 rays or streamers do not return ; they separate and soon be- 

 come too diffused to be any longer visible, and may well go 

 to furnish the matter of the zodiacal light, which otherwise 

 has not received a satisfactory explanation. And further, if : 

 such a force exist at the sun, the changes of terrestrial mag- 

 netism may be due to direct electric action as the earth moves 

 through lines of inductive force. 



These conclusions appear to be in accordance broadly with 

 the lines along which thought has been directed by the re- 

 sults of subsequent, eclipses. Professor Schuster takes an 

 essentially similar view, and suggests that there may be a 

 direct electric connection between the sun and the planets. 

 He asks further whether the sun may not act like a magnet 

 in consequence of its revolution about its axis. Professor 

 Bigelow has recently treated the coronal forms by the theory 

 of spherical harmonics, on the supposition that we see phe- 

 nomena similar to those of free electricity, the rays being 

 lines of force, and the coronal matter discharged from the 

 sun, or at least arranged or controlled by these forces. At 

 the extremities of the streams for some reason the repulsive 

 power may be lost, and gravitation set in, bringing the mat- 

 ter back to the sun. The matter which does leave the sun is 



