Sept. lo, 1874J 



NA TURE 



387 



rock surface either entirely or in places. This may render an 

 experiment, as that on cannel coal may not impossibly have been, 

 from this cause entirely valueless ; yet this result presents itself, 

 with many others met with in the investigation, as very well 

 wortli repetition, with fresh precautions and with new arrange- 

 ments to guard against the possiMlity of false conclusions. 



Adopting for the present, as probably not very far from the 

 truth, a common reduction factor of 2;-; as the proportion in which 

 the recorded temperature differences of the plain rock sur- 

 faces between velvet faces exceeded the true temperature 

 differences of the surfaces of the rocks examined, and intro- 

 ducing some very small corrections for the thicknesses of 

 the plates, the thermal capacity of the metal cooler, &c. , 

 which are all probably (as well as the allowance for heat- 

 absorption in raising the temperature of the rock plates very 

 slowly during the obsei'vatiors) really negligible in compari- 

 son with the uncertainty that attaches (except in one or two well- 

 observed cases of absolutely measured temperature differences of 

 the rock faces) to the great majority of the determinations from 

 unknown peculiarities of surface contact and temperature assimi- 

 lation where air is not excluded from the junctions, or rendered 

 stagnant in its mode of heat transmission, the following table 

 gives the absolute thermal conductivities (in centimetre-gramme- 

 second, or absolute British -Association units) thus provisionally 

 obtained, together with a few similar results found by Peclet, 

 Forbes, and Sir William Thomson in rocks differing little in their 

 description from those included in the present list. 



TheRtport of the Committee for nipcrintending the monthly reports 

 of the frogrcis of Chemistry, by Profs. Roscoe and Williamson, was 

 then read by Prof. Roscoe. The report was very short; the 

 committee does not intend to apply to the British Association 

 for a further grant after the present year. 



Report of the Committee on Essential Oils, by W. Chandler 

 Roberts. — The following oils have been examined : Wormwood, 

 Citronella, and Cajeput. The actions of phosphorus penta- 

 sulphide, of zinc chloride, and of bromine upon the oils were 

 described. The first-named reagent generally acts by removing 

 the elements of water, with formation of terpenes and cymenes. 

 Zinc chloridegenerally causes decomposition, giving rise to a mix- 

 ture of hydrocarbons. Bromine usually forms a bromide, which 

 is then decomposed with evolution of hydrobromic acid and water 

 and formation of a cymene. 



Various cymenes have been examined, all of which seemed to 

 be the same. The formation of cymenes from terpenes by the 

 action of sulphuric acid has been verified. Cymenes have also 

 been obtained from oil of turpentine by continued fractionation. 



The following numbers express the optical properties of some 

 of these oils : — 



Specific 

 refractive energy. Specific dispersion. 



Absinthol "4887 '0234 



Cajeput 'A9l(> '0251 



Citronella ... ... '5213 ... .. "0289 



Citronellol '5'76 '0284 



The conclusion drawn is, that cymene is the central body in 

 these essential oils, to which the other constituents are closely 

 related ; the varying amounts of mechanical energy required for 

 the formation of the different isomerides have not as yet been 

 determined. 



Dr. Gladstone said that the optical properties of sixteen cymenes 

 had been examined. Some of these were obtained from sub- 

 stances of low, others from substances of high refractive energy, 

 but in all cases the refraction of the cymene was the same ; the 

 refraction of a substance depends, therefore, on tlie constitution 

 of the substance itself. 



Report of the Committee on the Estimation of High Tempera- 

 tures, by J. Dewar, F.R.S. E. — The committee has not carried 

 on any investigations during the past year. 



Gold Assays, by W. Chandler Roberts. — Little has been done 

 by the committee during the past year, but they hope to be able 

 to report fully at the next meeting. 



Report of the Committee for assisting in the Exploration of tit 

 Victoria Cave, Settle, by R. H. Tiddeman, secretary to the 

 committee. 



The explorations have been continued throughout the chief 

 part of the year. The Settle Committee have raised by private 

 subscriptions and spent, besides the British Association grant of 

 50/., a sum of 113/. 4.f. 31/. The late determination of a bone 

 which had been found by the committee in the cave in May 

 1S72 as human, by so great an authority as Prof Busk, induced 

 the committee to pay their chief attention to the question of its 

 position and the relation of the beds in which it occurred to the 

 physical changes to which the district has been from time to time 

 subjected. In order to do this it was necessary to remove a 

 large portion of the tip of the older workings, which had unfor- 

 tunately accumulated below the entrance of the cave. Beneath 

 this the Romano-Celtic layer was reached, and several objects of 

 bronze, including bracelets, a vinaigrette, and other articles, were 

 obtained. The Romano-Cel'ic layer was from i ft. to i ft. 6 in. 

 thick ; beneath this was a thickness of 19 ft. of screes, consisting 

 of angular fragments of limestone, which had fallen from the 

 face of the cliff above. This contained no bones whatever, nor 

 the smallest fragment of any rock but the white limestone of 

 which the cliff above is made. But at the base of this a great 

 many boulders were discovered of all dimensions up to 7 ft. in 

 diameter. The number of these boulders and the peculiar con- 

 ditions of their position render it quite impossible that they can 

 have been brought through any fissure in the roof of the cave, 

 and so washed in later times over the beds containing the human 

 fibula and the remains of the older mammals. The great weight 

 of some of them quite mihtates against this idea. Another 

 suggestion, that they may not have been left in their present 

 position at the melting of the ice-sheet, but may have fallen from 

 the cliff in comparatively recent times, is also negatived by the 

 complete absence of any evidence of any such fall through the 

 long period represented by the 19 ft. of screes, their occurrence 

 only at the base of the screes, and by the absence of any drift 

 from the cliff above for some distance round. But another strong 

 argument against this supposition lies in the fact that the boulders 

 are so close beneath the cliff, that if all the limestone weathered 

 from the cliff above and now resting on the boulders were re- 

 stored to the cliff it would project so much further forward that 



