NA TV RE 



481 



THURSDAY, APRIL 18, 1878 



THE COMING TOTAL SOLAR ECLIPSE 

 n^HERE is no doubt whatever that the eclipse which 

 -1- will sweep over the United States next July will be 

 observed as no eclipse has ever been observed before. 

 The wealth of men, the wealth of instruments, and the 

 wealth of '.skill in all matters astronomical, already accu- 

 mulated there, makes us Old Country people almost gasp 

 when we try to picture to ourselves what the golden age 

 will be like there, when already they are so far ahead of 

 us in so many particulars. 



Draper, Hall, Harkness, Holden, Langley, Newcomb, 

 Peters, Peirce, Pickering, Rutherfurd, Trouvelot, and 

 last, but not least, Young, are the names that at once 

 run easily off the pen to form a skeleton list, capable of 

 considerable expansion with a little thought, when one 

 thinks of the men who will be there. One knows too 

 that all the enthusiasm of devoted students and all the 

 appliances of modern science— appliances in the creation 

 of which many of those named have borne so noble a 

 part — will not be lacking. So that we may be sure that 

 not only all old methods but all possible new ones will be 

 tried to make this year one destined to be memorable in 

 the annals of science side by side with 1706, 185 1, i860, 

 and other later years. 



Thank Heaven, too, there isno necessity that the thank- 

 less task of organising an "Eclipse Expedition" from 

 this country should fall on any unfortunate individual, 

 among other reasons because— and this is a very hopeful 

 sign of increasing general interest taken in scientific 

 work — Messrs. Ismay, Imray and Co., the owners of the 

 White Star Line, have expressed in the warmest manner 

 their desire to aid English observers by a considerable 

 reduction of fares, and the directors of the Pennsylvanian 

 Railway Company, as the readers of Naturk have 

 already been made aware, have done the like in the case 

 of observers coming from Europe in their individual 

 capacity.^ 



The progress in that branch of knowledge which 

 requires the aid of eclipse observations has been so rapid 

 during the last few years that the eclipse of 1868, though 

 it happened only ten years ago, seems to be as far 

 removed from the present as the Middle Ages are in 

 regard to many other branches of culture. The work 

 done by the spectroscope since that year, when in the 

 hands of Janssen, Pogson, Herschel, and others, it 

 added so enormously to our knowledge, has gradually 

 covered larger and larger ground, and each successive 

 eclipse in 1869, 1870, 1871 and 1875, has seen some 

 variations in its use, so that its employment has proved the 

 most novel, if not the most powerful, side of the attack. 



Young's work of 1869 will no doubt form the key-note of 

 much that will be done this year so far as the coronal atmo- 

 sphere is concerned. It will be remembered that Young 

 in 1869 observed a continuous spectrum, while Janssen in 

 1 87 1 observed a non-continuous one, for he recorded the 

 presence of the more prominent Fraunhofer lines, notably 

 I). This positive observation from so distinguished an 



« In fact Messrs. Ismay, Imray and Co. have just announced that they 

 will take properly certified observers and bring them home again for the sum 

 of 20/., which is rather less than" ist class single fare; so that Knglish 

 observers wdl be carried to Denver or the Rocky Mountains and back again 

 for the suni of 34/. 



Vol. XVII. — No. 442 



observer demands attention, not only on its own account, 

 but because of the question which hangs upon it, which 

 is this : Does the corona reflect solar light to us or does 

 it not, and if it does, where are those particles which thus 

 act as reflectors ? On this point the photographs taken 

 in Siam in 1875 are silent, as the method employed was 

 not intended to discriminate between a continuous and a 

 discontinuous spectrum. 



But although this point remains, how greatly has 

 the ground been cleared since 1869, That wonderful 

 line, " 1474," is more familiar to us now ! and yet there 

 has been almost a chapter of accidents about it. In the 

 first place, with regard to this line above all others, 

 there appears to be a mistake in Angstrom's map; 

 the solar line at 1474 is not due to iron at all; with 

 the most powerful arc there is no iron line to be seen 

 there. Then Secchi attributed it to hydrogen, though I 

 am not aware on what evidence. But whatever be its 

 origin, the fact remains that we now know by its means 

 that the solar hydrogen is traversed and enwrapped by 

 the substance which gives rise to the line to an enormous 

 height, so that it forms the highest portion of the atmo- 

 sphere which is hot enough to render its presence 

 manifest to us by spectral lines. Here, so far as I know, 

 only one point of difference remains. In 1871 I most 

 distinctly saw the line trumpet-shaped, that is, with the 

 base broadening as the spectrum of the photosphere was 

 reached, while Janssen saw it stopping short of the spec- 

 trum of the photosphere. The importance of this point is 

 that supposing one of us to be mistaken and one or other ob- 

 servation to represent a ^t';/j^rt«/ condition, then, if the line 

 broadens downwards till the sun is reached we are dealing 

 with a gas lighter than hydrogen, capable of existing at a 

 high temperature, which thins out as the other gases and 

 vapours do in consequence of its vapour density being 

 below that of hydrogen ; or, on the other hand, if the line 

 stops short as a constant condition, it represents a sub- 

 stance which is probably dissociated at the lower levels, 

 and is therefore probably a compound gas ; and then the 

 question arises whether it has not hydrogen as one of its 

 constituents. 



Perhaps I may conveniently refer to a paper of mine 

 which was read at the Royal Society last Thursday in 

 this connection, because it may be that the solar regions 

 most worthy of the closest study at the present time are 

 precisely these higher reaches of the sun's atmosphere. 

 There is little doubt, I think, that around the sun's visible 

 atmosphere matter exists at a temperature low enough not 

 to give us its autobiography in the bright line manner, 

 and there is evidence that matter existing under such 

 conditions, absorbing as it must do some of the sun's 

 light, will, if it remains elemental, give us an absorption 

 of the fluted kind, or again will absorb only in the blue 

 or ultra-violet region. 



Now the more the chemistry of the reversing lower 

 layer of the sun's atmosphere— that in which the uppei^ 

 level of the photosphere is bathed— is examined the more 

 metallic is it found to be. For instance, my own work 

 has enabled me to trace with more or less certainty 

 eighteen metallic elements,^ in addition to those recorded 



I These are strontium, lead, cadmium, potassium, cerium, uranium, vana- 

 dium, palladium, molybdenum, indium, lithium, rubidium, cccsmm, bismuth, 

 till, lanthanum, glucinuni, and yttrium or erbium. 



