Jaxiaby 1, 1900.] 



KNOWLEDGE 



13 



to iuvestigatiou. The photographs takcu during reoent 

 eclipses, some of which are fiuuiliar to the readers of 

 Knowledge, give very complete data as to chromo- 

 sphere, promiueuces, aud corona, and for our present 

 purposes we may take these as including practically all 

 that is certainly known of these appendages. 



These photographs indicate that the chromosphere in 

 its upper parts — live or sis thousand miles above the 

 photosphere — consists chiefly of livdrogcu, helium, and 

 calcium, while at lower levels we get indications ot 

 metallic substances in tlie numerous lines which consti- 

 tute the so-called " flash " spectrum. As is now well- 

 known, the flash spectrum is not a simple reversal of 

 Fraunhofcr lines : while the majority of the 25i"inrip<i' 

 dark lines probably have corresponding bright lines in 

 the flash spectrum, a great number of bright lines not 

 represented with proper intensity by dark lines make 

 their appearance (fig. 1). Sir Norman Lockyer has traced 

 many of these bright lines to known substances, such as 

 iron, titanium, and so on. He has shown that tiles'? 

 previously " unknown" lines of the chromosphere spec- 

 trum are mostly lines which become intensified, or 

 ■' enhanced." when we compare a spark with an arc 

 spectrum of the same substance, and in the present 

 stage of the inquiry it is supposed that the enhance- 

 ment of these lines is due to the higher temperature of 

 the spark. If we grant that the region which pro- 

 duces the flash spectrum is at a temperature higher than 

 that which by its absorp'tion produces the Fraunhofer 

 lines, we not only have a pretty complete explanation 

 of the origins of the lines, but we have a reason for the 

 want of similarity between the flash and the Fraun- 

 hofer spectra. So far as there is any similarity between 

 the two, it may reasonably be ascribed to the fact that 

 the same substances are involved in the production of 

 the dark and bright line spectra, and that many lines 

 persist through a great range of temperature. But 

 whatever may be the physical explanation, the dis- 

 covery of the enhanced lines, aided by that of helium, 

 removes a great deal of the supposed non-terrestrial 

 matter from the chromosphere, and there is probably 

 now no greater a percentage of unfamiliar lines in the 

 chromosphere than in the solar spectrum itself. 



The spectra of the prominences show that the sub- 

 stances present are the same as those which exist ii 

 the chromosphere, no additional elements being cei'- 

 tainly indicated. 



When we come to the corona, however, we have still 

 to acknowledge ourselves in the region of the unknown. 

 First and foremost in its spectrum is the green line 

 which has, until quite recently, been known as 1474K, 

 but which we now know to be much more refrangible 

 than this line. Photographs taken at Viziadrug, India, 

 in 1898, (fig. 1), show that while the bright 1474K line 

 is truly chromospheric (Lambda 5316.79) and corres- 

 ponds to an enhanced line of iron, that of the corona 

 has a wave length 5303.7.* and has not yet been identi- 

 fied, unless Prof. Nasini's supposed new gas from 

 Pozzuoli turns out to be its terrestrial equivalent. As 

 to the other coronal lines which have been photographed 

 during recent eclipses, no satisfactory evidence as to 

 their origin is forthcoming, but the discovery of helium 

 encourages us to hope that the coronal gases will be 

 also eventually found upon earth. 



In the present state of our knowledge it does not 

 seem possible to give a perfectly trustworthy list of the 

 elements certainly present in the sun. One published 



• Hoy. Soc. Proc, Vol. LXIV., p. 168. 



by Rowland, in 1891, is the most extensive, but the 

 more recently published tables do not seem to afford 

 complete justification for it. Taking the tables, how- 

 ever, and including oxygen, gallium, and the chromo- 

 spheric and coronal gases, we may summarise the most 

 probable elements as follows : — 



Alumiuiuiii 



■AsU'viutiit 



BiLritiin 



Ciulmium 



Calcium 



C'arbou 



Cerium 



Cobalt 



Cop])pr 



Coronium* 



Chromium 



Jt.ydrogoM 



Heliumt 



I rou 



Lunthanuui 



Magnesium 



Manganese 



Molvlidenum 



Neodymium 



Nickel 



Oxygen 



Palladium 



I'otassiinu 



Scandium 



Silicon 



Silver 



Sodium 



Strontium 



Titanium 



Vanadium 



Yttrium 



Zinc 



Zirconium 



In addition there is evidence which suggests the 

 [jossible presence of the following elements : — 



Bervllium 



Didymium 



Krbiuni 



Indium 



Lead 



Mercury 

 Niobium 

 I'latiuum 

 Rhodium 



Ruthenium 

 Thallium 

 Tin 

 Tungsten 



Besides these, Rowland, in his 1891 list, includes 

 germanium and glucinum among the elements present, 

 and iridium, osmium, tantalum, thorium, and uranium 

 among those doubtfully present, while Lockyer con- 

 cluded that lead and uranium were certainly present, 

 and lithium, glucinum, rubidium, cresium, and bismuth 

 probably present. 



It will be seen that the constituents of the sun 

 approximate to those of our own earth, and Prof. 

 Rowland was probably not far from the truth when he 

 remarked some years ago that " were the whole earth 

 heated to the temperature of the sun its spectrum 

 would probably resemble that of the sun very closely." 

 In each case our knowledge is fragmentary. Our ter- 

 restrial chemistry is but skin deep, and our solar 

 chemistry is only that of the sun's atmosphere, for we 

 as yet know nothing either of the interior of the earth 

 or of the vast region which lies beneath the sun's 

 photosphere. It must be borne in mind also that as 

 regards the sun our knowledge is limited to the indi- 

 cations of the spectrum, which in the case of a mixture 

 of substances may render no account of some of the 

 elements present. Thus, although we are not yet in a 

 position to assert that the composition of the stin is 

 identical with that of the earth, it would not be easy 

 to justify the view that there is any fundamental dif- 

 ference. 



[For the tise of figures 1 and 3 we are indebted to 

 Sir Norman Lockyer, and for figures 2 aud 4 to 

 editors of the " Astrophysical Journal."] 



the 



"TREES STRUCK BY LIGHTNING." 



By Howard B. Little. 



Throughout the past year correspondence has 

 been carried on under the above heading in Knowledgk. 

 It was in January last that " A. C. " gave an account 

 of an elm tree which had been practically shattered by 

 the dread stroke; and he asked, '^ What actually takes 

 place? What is the force exerted?" In the following 

 month, again on the correspondence page, I answered 

 these questions to the best of my ability, pointing out 

 that our ascertained facts were few, but that electro- 



* In corona ouly. t In cliromosphere only. ( Asterium and helium, 

 ccording to Lockyer. are the two constituents of the eleveite gas.) 



