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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



portance that these data should be accumulated, 

 more especially, because it has been found that 

 both in the case of spots and prominences there 

 are distinct cycles which, in the future, may not 

 only be very much fuller of meaning to us than 

 they seem to be at present, but may even satisfy 

 the representatives of the cui bono school who, I 

 suppose, see in Priam's treasure but so many 

 ounces of gold. 



This brings me to refer to the second branch 

 of the work ; and it is this : These various cycles 

 of the spots and prominences have long occupied 

 the attention both of meteorologists and magneti- 

 cians ; and one of the most interesting fields of 

 modern inquiry, a field in which very consider- 

 able activity has been displayed in the last few 

 years, is one which seeks to connect these various 

 indications of changes in the sun with changes in 

 our own atmosphere. 



The sun, of course, is the only variable that 

 we have. Taking the old view of the elements, 

 we have fire represented by our sun, variable if 

 our sun is variable ; earth, air, and water, in this 

 planet of ours, we must recognize as constants. 

 From this point of view, therefore, it is not at all 

 io be wondered at that both magneticians and 

 meteorologists should have already traced home 

 to solar changes a great many of the changes 

 with which we are more familiar. This second 

 line of activity depends obviously upon the work 

 done in the first, which records the number (the 

 increasing or decreasing number) of the spots and 

 prominences, and the variations in the positions 

 which these phenomena occupy on the surface 

 of the sun. As a result of this work, then, we 

 shall have a complete cataloguing of everything 

 on the sun, and a complete comparison of every- 

 thing which changes on the sun with every me- 

 teorological phenomenon which is changeable in 

 our planet. Some of these comparisons I have 

 already had an opportunity of discussing in these 

 pages in conjunction with my friend Dr. Hunter. 



When we come to the third branch of the work, 

 the newest parallel in the quiet sap to which I have 

 already referred, things arc not in such a good 

 condition. The miners are too few; and one of 

 the objects of any one who is interested in this 

 kind of knowledge at the present moment must 

 be, to see if he cannot induce other workers to 

 come into the field. 



The attempt to investigate the chemistry of 

 the sun, independently even of the physical prob- 

 lems which are, and indeed must be, connected 

 with such an inquiry, is an attempt almost to do 

 the impossible, unless a very considerable amount 



of time and a very considerable number of men 

 be engaged upon the work. If we can get as 

 many investigators to take up questions dealing 

 with the chemistry of the sun as we find already 

 in other branches of knowledge more closely con- 

 nected with the old curriculum of studies, we may 

 be certain that the future advance of our knowl- 

 edge of the sun will be associated with a future 

 advance of very many of those very problems 

 which, at the present moment, seem absolutely dis- 

 connected and indeed distract attention, from it. 



I have, in the present paper, to limit myself 

 to this chemical branch of the inquiry; and I 

 shall begin by referring to the characteristics of 

 the more recent work with which I shall have to 

 deal. 



Here, as in other regions of physical and 

 chemical inquiry, advance depends largely upon 

 the improved methods which all divisions of sci- 

 ence are now placing at the disposal of all others. 

 Our knowledge of the chemical nature of the 

 sud is now being as much advanced by photog- 

 raphy, for instance, as that descriptive work of 

 which I wrote in the first instance, which deals 

 with the chronicling and location of the various 

 phenomena, has, in its turn, been advanced by 

 the aid of photography. The increased power in 

 this direction recently realized by Dr. Janssen is 

 one which was absolutely undreamed of only 

 a few years ago. It is now possible to record 

 every change which goes on on the sun down to 

 a region so small that one hardly likes to chal- 

 lenge belief by mentioning it. Changes under 

 one second of angular magnitude in the centre 

 of the sun's disk can now be faithfully recorded 

 and watched from hour to hour ; in other words, 

 changes in cloud-regions ten miles square in a 

 body 92,000,000 miles away can now be chron- 

 icled. 



One of the advantages which has come from 

 the introduction of new apparatus has been the 

 possibility of making maps of the solar lines and 

 of the metallic lines which have to be compared 

 with them on a very large scale. Thanks to the 

 generosity of Mr. Rutherfurd, the distinguished 

 American astronomer, who is making the most 

 magnificent diffraction-gratings which the world 

 has ever seen, and who is spreading them broad- 

 cast among workers in science, we have now 

 easy means of obtaining with inexpensive appa- 

 ratus a spectrum of the sun, and of mapping it 

 on such a scale that the fine line of light which 

 is allowed to come through the slit is drawn out 

 into a band or spectrum half a furlong long. A 

 complete spectrum on this scale, when complete 



