176 



NA TURE 



\yuly 2, 1874 



apparent than in the corresponding case of water. This agrees 

 well with the explanation ; for, as previously shown, the effect 

 of mercury would for the same quantity of heat be three times 

 as great as that of water ; and besides tliis, ttie perfect slate of 

 the vacuum would allow the pith (or whatever the ball might 1 

 be) to move much more freely than when in the vapour of water 

 at a considerable tension. 



Of course the reasoning is not confined to mercury and water ; 

 any gas which is condensed or absorbed by the balls when cold 

 in greater quantities than when warm would give the same 

 results ; and as this property appears to belong to all gases, it is 

 only a question of bringing the vacuum to the right degree of 

 tension. 



There was one fact connected with Mr. Crookes' experiments 

 which, independently of the previous considerations, leads me to 

 the conclusion that the result was due to the heating of the pith, 

 and was not a direct result of the radiated heat. 



In one of the experiments exhibited at the Soiree of the Royal 

 Society, a candle was placed close to a flask containing a bar 

 of pith suspended from the middle ; at first the only thing to 

 notice was that the pith was oscillating considerably under the 

 action of the candle ; each end of the bar alternately approached 

 and receded, showing that the candle exercised an influence 

 similar to that which might have been exercised by the torsion of 

 the thread had this been stiff. After a few mi.iutes observation, 

 however, it became evident that the oscillations continued instead 

 of gradually diminishing, as one naturally expected them to do; 

 and, more than this, they actually increased, until one end of the 

 bar passed the light, after which it seemed quieter for a little, 

 though the oscillations again increased until it again passed the 

 light. 



The explanation given is tha^, owing to the slowness with 

 which the pith takes in and gives out heat, its ends will on the 

 whole be hotter while receding from thin while approaching the 

 candle, and hence the force, as a mean, will be greater on that 

 end which is receding, and there will be a continual oscillation. 



Since writing the above paper, it has occurred to me that, 

 according to the kinetic theory, a somewhat similar effect to that 

 of evaporation must result whenever heat is communicated from 

 a hot surface to gas. 



The particles which impinge on the surface will rebound with 

 a greater velocity than that which they approached, and conse- 

 quently the effect of the blow must be greater than it would have 

 been had the surface been of the same temperature as the gas. 



And in the same way whenever heat is communicated from a 

 gas to a surface the force on the surface will be less than it 

 otherwise would be, for the particles wid rebound with a less 

 velocity than that at which they approach. 



It is then shown mathematically, that for every English unit 

 of heat communicated to steam at a temperature of 60°, the re- 

 action on the surface is equivalent to ^S lb. acting for one 

 second ; and in the same way for air the force is equivalent to 

 ■55 lb. It is also pointed out that since the diffusion of heat 

 within a gas is inversely proportional to its density, the amount of 

 . heat communicated from a su; face to the surrounding gas is inde- 

 pendent of the density of the gas, and hence, that the reaction 

 on the pith in Mr. Crookes' experiments would remain constant 

 as the vacuum improved, while the counteracting forces would 

 diminish and leave the balls more free to move. It is therefore 

 assumed that the results obtained in those experiments might have 

 been at least in part due to such forces. 



Linnean Society, June 19. — Dr. G. J. Allman, F.R. S., presi- 

 dent, in the chair. — Mr. D. Hanbury, treasurer, exhibited branches 

 of olive grown in the open air at Clapham, some bearing flowers, 

 others nearly ripe fruit ; also a specimen of Khmm officinale 

 Baill., now grown in this country for the first time, the source of 

 the true medicinal Turkey rhubarb, and pointed out the charac- 

 ters in which it differs from other species of the genus. — Dr. 

 Hooker made a communication on the subject of some India 

 Ganiitias to the effect : — (l) That the G. indica Chois. (pnrpwea 

 Roxb.), had been placed in a wrong section in Anderson's review 

 of the genus in the "Flora of Ijritish India." (2) That the 

 plant described in the same work as G. i^riffitlni is proved to be 

 the true Gamboge plant of Siam, G. piiu-lla, var. pcdicellnta of 

 Hanley, which Dr. Hooker regards as a distinct species, and 

 proposes that the name of G. hanlniryi should be given to it. 

 (3) That tliC (■/'. hn-z'iivslris of Scheflfer is identical with G. 

 eugeniitfoAa of Wallich. (4) That the name of G. oi.alifolia 

 Hook, f., must give place to the previously published G. ova/i- 

 /(j/w of Oliver's -'Flora of Tropical Africa;'' and the Indian 



plant must take the name of spicata, it being a form of Xantho- 

 chymus spicaliis W. et A. — Prof. Thiselton Dyer exhibited a 

 young oak-plant with three cotyledons, wliich had been sent to 

 him by Mr. Cross, of Chester ; also a pitcher-like development 

 of a leaf of the common cabbage, from Ilarting, Sussex, sent by 

 Mr. H. C. Watson to the Kew Museum. — Mr. A. W. Bennett 

 exhibited drawings of the style, stigma, and pollen-grain of 

 J-'rijt^ica antiscorbutica Hook, f., describing the remarkable 

 manner in which the pollen of Priiiglm differs from that of other 

 nearly allied Crucifers, being much smaller and perfectly spheri- 

 cal, instead of elliptical with three furrows. This he considered 

 a striking confirmation of Dr. Hooker's suggestion that we have 

 here a wind-fertilised species of a family ordinarily self-fertilised, 

 ahypothe.-is which is again confirmed by the total absence of hairs 

 on the style of Prini;lca. — An extract was read of a letter from Mr. 

 Harry Bolus to Dr. Hooker, F. RS., dated GraafReinet, April 4, 

 1S74, in which he comments adversely on some of the reasonings 

 contained in Grisebach's " Vegetation der Erde" in favour of 

 the theory of "independent centres of creation." Grisebach, 

 relying chiefly on an observation of Burchell'?, makes the Orange 

 river the boundary between the Cape and Kalahari provinces, a 

 boundary which Mr. Bolus shows to be untenable, at least in 

 certain portions. Grisebach unites the Kanoo flora with that of 

 the Cape province ; while Mr. Bolus doubts whether it does not 

 differ more from this than from the Kalahari. The Roggeveld, 

 and indeed the whole Kanoo, by its predominance of shrubby 

 Compositx, seems to incline more to the desert type of plants 

 than to the richer Cape flora. — The following papers were then 

 read, viz. ;--Oa the resemblances between the bones of typical 

 living 1 e,. tiles and the bones of other animals, by Harry G. Seeley. 

 — On the Auxemmea;, a new tribe of Cordiacece, by J. Miers. 

 — A revision of the sub-order Mimoseas, by G. Bentham, LL. D. — 

 On some fungi collected by Dr. S. Kurz in Vomah, Pegu, by F. 

 Carrey. — Notes on the letters from Danish and Norwegian natu- 

 ralists contained in the Linnean correspondence, by Prof J. C. 

 Schiodte, of Copenhagen. 



Geological Society, June 10.— John Evans, F.R. S., pre- 

 sident, in the chair. — Tlie following communications were read : 

 — On the occurrence of Thanet-beds and a crag at Sudbury, 

 Suffolk, by William Whitaker. After referring to some passages 

 in papers by Mr. Prestwich, in which the probable existence of 

 Thanet-beds in North Essex is mentioned, the author described 

 certain sections near Balingdon, on the right bank of the Stour, 

 which exhibit sands belonging to this series. The crag-beds 

 described by the author are found on the left bank of ihe ttour, 

 in Suffolk, and consist of ferruginous dark reddish brown sand, 

 with Layers of ironstone, slightly false-bedded, with here and 

 there light-coloured grit with broken shells. — Notes on the phe- 

 nomena of the t^uaternary Period in ihe Isle of Portland and 

 around Weymouth, by Joseph Prestwich, F.R.S. Commencing 

 with the oldest drift-beds, the author showed that the remains of 

 one, formerly more extensive, had been found in the Isle of 

 Portland at a height ot 400 ft. above the sea ; that it contained 

 the remains of the EUphas aiiliquus, Equiis Jossilis, iS:c. ; and 

 that he fouvid in this bed a number of pebbles of sandstone and 

 ironstone of Tertiary age, and of chert from the Greensands, 

 whence he inferred that, as such pebbles could not now pass ovtr 

 the plain of Weymouth, they must have done so beore that area 

 was denuded, and when bridged over by the Portl.md and Pur- 

 beck beds ; for the pebbles are derived from beds which are only 

 in situ to the north of the Weymouth district, and at a distance 

 of eight to ten miles from Portland. Further, this transport 

 must have taken place before the elevation of the north end of 

 Portland, and when the slope from the Bill to the Ridgeway was 

 uniform and gradual. The anticlinal line, which has elevated 

 the intermediate area, must be of later date than the drift-bed. 

 The author next proceeded to notice the raised beach at the Bill 

 of Portland, in which he had, with the assistance of Mr. Jeffreys, 

 determined twenty-six species of shells, two of them not now 

 living in the British Channel, and one new. This beach con- 

 tains pebbles of the Devonshire and Cornwall rocks. The raised 

 beach Mr. Prestwich found to abut .against an old cliff that had 

 been swamped at a later geological period by a land-wash, which 

 had levelled it and the old sea-land with ihe adjacent land- 

 surface. The mass which had thus swamped the cliff and buried 

 the beach consisted of loam and angular dcinis, the latter being 

 in larger proportion at top. In the loam he found several species 

 of land and fresh-water shells and fr.agments of bones. Phe 

 angular di'hris consisted of pieces of the local rocks, together 

 with a number of specimens, which by their organic remains were 



