Mineral Constituents of Dust ancl Soot from various Sources. 97 



the lines of any metal varies with the amount of the metal in the 

 charge, but in some cases variations of intensity occur among the 

 lines of one metal as observed in the spectra photographed at Crewe 

 in 1893 ; especially is this the case with some lines in the visible 

 spectrum of iron. 



These variations are due to changes in temperature ; as the tempera- 

 ture of the flame rises, some lines fade almost away, others become 

 stronger. The changes are more marked in the arc spectrum and still 

 more in the spark spectrum of iron. 



Lines of potassium and the edges of manganese bands are shown to 

 have been intensified by the proximity of iron lines in some cases, but 

 this is doubtless a result of low dispersion. The two violet rubidium 

 lines nearly coincide with two lines of iron.* 



A new line of potassium with, variable intensity. This line, wave- 

 length approximately 4642, varies in intensity within somewhat wide 

 limits. In a given name its brilliancy is increased by diminishing the 

 quantity of metallic vapour in the flame : this does not appear to 

 depend altogether on the weakening of the continuous spectrum ; it is 

 probably clue, in part at least, to the increased freedom of motion 

 permitted to the molecules of the metal. 



" The Mineral Constituents of Dust and Soot from various 

 Sources." By W. K Hartley, F.R.S., Royal College of 

 Science, Dublin, and Hugh Ramage, A.R.C.So.L, St. John's 

 College, Cambridge. Received November 20, 1900 — Read 

 February 21, 1901. 



Baron Nordenskjold has described three different kinds of dust 

 which were collected by him.f Of two of these, one consisted of 

 diatomacese and another of a silicious ancl apparently felspathic sand : 

 both were found on ice in the Arctic regions. The third variety was 

 quite different and appeared to be of cosmic origin. He observed that 

 some sand collected at the end of a five or six days' continuous fall 

 was mingled with a large quantity of sooty-looking particles, consist- 

 ing of a material rich in carbon. It appeared to be similar to the 

 dust which fell, with a shower of meteorites, at Hessle near Upsala 

 in the beginning of the year 1869. As in this particular instance it 

 might be supposed that the railways and houses of Stockholm had 

 contributed some of this matter to the atmosphere, and that the snow 

 had carried it down, he requested his brother, who then resided in a 

 desert district of Finland, to give his attention to the subject, with 



* ' Eoj. Dublin Soc. Proc.,' vol. 8 (X.S.), Part YI, p. 705. 

 f ' Gomptcs Rendus/ vol. 78, p. 236. 



