742 Prof. H. E. Armstrong on Low-Temperature Research 



In this connexion, attention may be called to the question I have 

 raised, in m v previous essay, as to the constitution of the black forms of 

 carl)on : it was tliere argued that probably the molecule is one of great 

 complexity.* I would now add that it is in no way certain that any 

 form of black " carbon " is an elemental substance and not a highly 

 " condensed " hydrocarbon containing a very small atomic proportion 

 of hydrogen. The practical impossibility of getting rid of hydrogen, on 

 wliich Professor Dewar has laid such stress, is in favour of this view. 



In the same lecture the multiple spectra of magnesium were con- 

 sidered and the conclusion arrived at that no satisfactory evidence 

 of elementary dissociation could be deduced from the variations. 



Finally, the apparent identity of spectral lines was discussed and 

 a number of supposed coincidences shown to be non-existent, the 

 final conclusion being that the few as yet unsolved coincidences 

 either would yield to a higher dispersion or are merely accidental. 



This lecture is reported at unusual length in the Proceedings. 



The decay of interest in experimental spectroscopic inquiry of late 

 years is due, probably, in large measure, to the fact that each instru- 

 mental improvement made possible by the use of higher dispersive 

 power only serves to make any definite conclusion as to the coincidence 

 of lines supposed to be characteristic of different elements more and 

 more difficult to draw. Spectroscopy has now entered upon a new 

 phase and has been made the subject of mathematical speculation, 

 particularly since it has been held that even the atoms are of complex 

 structure. In the mind of the physicist, the observed breakdown of 

 materials such as thorium and uranium has added strength to the 

 conviction that the so-called elements generally are composite 

 materials, but the remarkable fact has to be taken into account that 

 by no means knoAvn to us can we either assist or promote the break- 

 down. The speculations rife in earlier years as to the decomposition 

 of the elements at high temperature, therefore, derive no support 



* The problem of the constitution of the carbon molecule has acquired 

 fresh interest, in che interval, owing to the discussion of the relationship 

 between the forms of crystals and their molecular structure. Barlow and 

 Pope have applied geometrical principles, whilst the Braggs have developed a 

 refined method of analysis involving the use of X-rays. The structure assigned 

 to the diamond is in accordance with chemists' views. The difference between 

 the diamond and the other supposed forms of carbon is so great that proof that 

 these are in reality hydrocarbons would be welcome. 



In this connexion, special reference mav be made to the lecture on " Recent 

 Researches on Meteorites," delivered by Prof. Dewar on June 11, 1886. Atten- 

 tion was then directed to the considerable amoimts of hydrogen and of the 

 hydrocarbon methane, CH^, given off not only from pieces of meteorite but also 

 various graphites, including that prepared by the action of oxidizing agents on 

 the cyanogen compounds in crude caustic soda, when heated in vacuo. The 

 conditions were not those under which methane could well be formed from 

 hydrogen and carbon. 



