60 REPORT—1904. 
temperatures of the day is only 12°-0, or less, the calculated sea-level - 
pressure for the top of the mountain is markedly greater than at Fort 
William, and the accompanying meteorological conditions are anti- 
cyclonic, the weather being clear, dry, and practically rainless ; (2) when 
the difference of temperature is 18°-0, or greater, the meteorological 
conditions are cyclonic, and the accompanying weather dull, humid, and 
rainy. 
The large result here arrived at empirically is in accordance with the 
principle laid down by Dalton—viz., that air charged with vapour or 
vaporised air is specifically lighter than when without the vapour ; or, 
in other words, the more vapour any given quantity of atmospheric air 
has in it the less is its specific gravity. 
Another important result is that the cases of small differences of 
temperature between the two Observatories are chiefly occasioned by an 
increase of temperature at the top of the mountain, and large differences 
of temperature by a decrease of temperature at the top. 
The intimate relation thus disclosed between the varying temperatures 
and sea-level pressures of a high-level and a low-level station is of 
prime importance in forecasting the weather, inasmuch as it reveals, in 
a way not hitherto attempted, the varying conditions of the hygrometric 
states of the atmosphere, particularly at high levels, upon which changes 
of weather so largely depend. The setting in of a process of saturation 
of the atmosphere at great heights may thus be made known, even when 
no cloud has yet been formed to indicate any such saturation. The 
important bearing of these results on such practical problems in meteoro- 
logy as the forecasting of the monsoons of India is evident. 
The Study of Hydro-aromatie Substances.—Report of the Committee, 
consisting of Dr. E. Divers (Chairman), Dr. A. W. CRossLEY 
(Secretary), Professor W. H. Perkin, Dr. M. O. Forsrer, and 
Dr. H. R. Le Svevr. 
Recent Work on Hydro-aromatic Substances. 
By Dr. A. W. Crossiey. 
Tue following is a summary of the work published on hydro-aromatic 
compounds since the preparation of the last report.! 
Petrolewm.— Roumanian petroleum ? resembles Russian and American 
petroleum, inasmuch as the densities of fractions taken every 2° between 
50° and 70° diminish to a minimum at 60° to 62°, and then continuously 
increase, whilst in the case of Galician oil there is a steady increase of 
density throughout. A further difference from this latter oil is to be 
found in the composition of the fractions between 60° to 100°, which do 
not contain secondary hexanes, as on nitration they yield aromatic deriva- 
tives only. Methyl- and ethyl-hexahydrobenzene are among the hydro- 
carbons contained in the Roumanian oil. 
Hydrocarbons.— Sabatier and Senderens* have shown that, when 
benzene or its homologues, containing methyl groups as side-chains, are 
passed together with hydrogen over reduced nickel, hydrogenation takes 
place without complication ; whereas if the hydrocarbons contain longer 
' Reports, 1903, p. 179. ? Poni, J. C. S., 1903, Abst. (1), 593. 
3 Compt. Rend., 1901, 182, 1254. 
