February 9, 1899] 



NA TURE 



543 



that the cleveite gases, which 1 obtained by the process 

 of distillation, accounted to a very great extent for the 

 first set. 



In 1897 in a series of three communications to the 

 Royal Society,' 1 pointed out that some of the other set 

 ■of unknown lines in the stars of intermediate temperature, 

 taking a Cygni as an example, were due to the enhanced 

 spark lines of iron and other metals, the arc lines being 

 almost entirely absent. 



During the last year, this research has been continued ; 

 and latterly, by the kindness of Mr. Hugh Spottiswoode, 

 the photographs of the enhanced lines have been ob- 

 tained by the use of the large induction coil, formerly 

 belonging to Dr. Spottiswoode, P.R.S. I am anxious to 

 ■express here my deep obligation to Mr. Hugh Spottis- 

 woode for the loan of such a magnificent addition to our 

 ■instrumental aids. 



The spark obtained by means of the Spottiswoode coil 

 is so luminous that higher dispersions than those formerly 

 •employed can be efl^ectively used, and in consequence of 

 this, the detection of the enhanced lines becomes more 

 €asy ; their number therefore has been considerably 

 increased. 



I shall deal in a subsequent communication, when the 

 inquiry has reached a further stage, with the details for 

 each element. 



The lines of the stars of intermediate temperature, like 

 a Cygni, have long been recognised by the Harvard 

 observers as well as by myself as presenting great 

 difficulties. 



In 1893 I wrote as follows' : "With the exception of 

 the K line, the lines of hydrogen and the high tempera- 

 ture line of magnesium at \4481, all the lines maybe 

 said to be at present of unknown origin. Some of the 

 lines fall near lines of iron, but the absence of the 

 strongest lines indicates that the close coincidences are 

 probably accidental." In the Harvard "Spectra of Bright 

 Stars," 1897, p. 5, the following words occur, relating to 

 the same stars : " This system of lines should perhaps be 

 regarded as forming a separate class, as in the case of 

 the Orion lines, and should not be described as 'metallic,' 

 as has just been done in the absence of any more dis- 

 tinctive name." 



From the fact that these unknown lines have now been 

 traced to a "proto-metallic" origin, as effectively as the 

 unknown lines of the hottest stars have been traced to 



3933'8 



.4219-0 



Comp.'irison of a Cygni and the enhanced lines of ( 

 A = spectrum of a Cygni betweeti wave-lengths stated. 



etals (chiefly of the iron group). 

 B = spectrum of enhanced lim 



The observations have already been mapped for the 

 following substances : — 



Iron, manganese, nickel, cobalt, magnesium, chromium, 

 ■calcium, strontium, copper, vanadium, titanium, silicon. 



In the accompanying photograph, a comparison is 

 shown between the lines of a Cygni and the enhanced 

 lines of the above substances thrown together. The ex- 

 traordinary number of coincidences is seen at a glance. 

 The facts are as follows : — 



The number of lines measured in the spectrum of a 

 Cygni at Kensington between \379S'i and A4S61 '6 



is ... 307 



Of these the number which approximately coincides 



with the enhanced metallic lines so far observed is 120 

 The number of lines (excluding the hydrogen series) in 

 a. Cygni of intensity over 4 (the maximum being 



represented by 10) is 40 



Of this number, the coincidences with enhanced 

 metallic lines with the dispersion employed 

 amount to ^8 



Roy. Soc. Proc, vol. 60, p. 475 ; ih'd., vol. 61, p. 14S ; i6id., 

 MI- 

 NO. 1528, VOL. 59] 



ol. 61 



helium and asterium, we may expect that the conse- 

 quences of this determination in relation to stellar classi- 

 fication and other connected matters, will be very far- 

 reaching. At present I am using this new spectrum con- 

 sisting of enhanced lines as an explorer, in relation to 

 some further details of stellar classification having special 

 reference to stars of Groups III. and IV. in which bright 

 as well as dark lines occur. 



HIGH ELECTROMOTIVE FORCE. ^ 

 T N the course of my investigation of electrical oscil- 

 -•■ lations I have been enabled, by a simple trans- 

 formation of my apparatus, to study electrical discharges 

 of greater intensity and length than have hitherto been 

 obtained in atmospheric air. These discharges are pro- 

 duced by means of a storage battery of ten thousand 



1 Pl:il. Trans., A, vol. 1S4, p. 694. 



- Extract from a lecture delivered by Prof. John Trowbridge before the 

 American Academy of Arts and Sciences, at a meeting held in the Jetferson 

 Physical Laboratory, Harvard University, Cambridge, U.S., December 14, 



