On the Spark Spectrum of Silicon as rendered by Silicates. 109 



Conclusions. 



(1.) The presence of nickel, as shown by the examination of soot, is 

 not positive evidence that the dust from the clouds comes from other 

 than a terrestrial source. 



(2) The dust which fell on the 16th and 17th of November, 1897, 

 with its regularity in composition and its similarity to meteorites, 

 being magnetic, also its comparative freedom from extraneous matter, 

 exhibits properties which are quite in favour of its cosmic origin. 

 Moreover, its composition is totally unlike that of volcanic dust and 

 flue dust from various chemical and metallurgical works. This dust for 

 the most part fell on a perfectly calm fine night, and there was no rain 

 for twenty-four hours or more afterwards,. 



We beg to draw attention once more to the very wide distribution 

 of gallium in minute proportions ; it occurs in all aluminous minerals, 

 flue dust of very different kinds, soot and atmospheric dust, also in a 

 great variety of iron ores. Bauxite contains it in larger proportion 

 than any other mineral, but the quantity even in this substance is very 

 small. We have hopes of finding it concentrated in some mineral, as 

 thallium, caesium, germanium, and indium are. Indium and thallium, 

 the other members of the same group of elements, are found in blende 

 and pyrites, and accordingly we might expect gallium to occur in a 

 concentrated state in a sulphide, arsenide, or similar compound. 

 Judging, however, from its analogy with aluminium, there does not 

 seem to be much probability of this. 



" Notes on the Spark Spectrum of Silicon as rendered by Sili- 

 cates." By W. N". Hartley, F.E.S. Received November 19, 

 1900— Read February 21, 1901. 



The interesting account by Mr. Lunt* of his identification of three 

 lines of silicon, corresponding with three unknown lines in the spectra 

 of certain fixed stars, contains the following remarks : — 



"It is a curious fact that Hartley and Adeney, and Eder and 

 Yalenta, who alone give us any extended list of lines due to silicon, 

 appear not to have examined the spectrum of this element in the 

 region of the three rays here considered. Their published wave- 

 lengths show only lines in the extreme ultra-violet, and the majority 

 of them are quite outside the region which can be examined by the 

 McClean star spectroscope." 



There is an inaccuracy here, and a similar mistake as to author- 

 ship occurs in the paper of Eder and Valenta. Silicon was not one of 

 the sixteen elements whose spark spectra were investigated by Hartley 

 * « Boy. Soc. Proc.,» vol. 66, p. 44. 



