142 



NA TURE 



[Dec. 9, 1886 



SOC/ET/ES AND ACADEMIES 

 London 



Royal Society, November 18. — " A Theory of Voltaic 

 Action." By J. Brown. Communicated by Lord Rayleigh, 

 Sec.R.S. 



The difference of potential near two metals in contact is due to 

 the chemical action of a film of condensed vapour or gas on their 

 surfaces. Such a pair of metals is thus similar to a galvanic 

 cell with its electrolyte divided by a diaphragm of air or other 

 gas, and it is the difl'erence of potential of the films that is 

 measured in " contact " experiments ; the metals themselves 

 being at one potential. 



Experiments with an electrometer h.aving quadrants of the 

 metals under examination, the construction of which was de- 

 scribed, were made on the rate of decrease of the difference of 

 potential near two metals in contact, and exposed to the action 

 of tlie air and of other gases ; also where a change in the con- 

 stiiuents of the atmosphere surrounding a pair of metals in con- 

 tact reverses the difference of potential near them in correspond- 

 ence with the reversal of electromotive force which takes place 

 after a similar change in the corresponding liquid electrolyte 

 used with the same metals as a voltaic cell. 



Such reversal takes place with pairs of copper-iron when 

 hydrogen sulphide gas, or ammonia gas, is added to the air 

 surrounding them ; with silver-iron, when hydrogen sulphide is 

 added ; and with copper-nickel when either ammonia or hydro- 

 chloric acid gas is added. 



Neutral or inert gases have little or no effect. 



Covering the metals with varnish, or immersing them in 

 naphtha, to protect them from atmospheric action, reduced the 

 difierence of potential near them considerably, but not to zero. 



Drying the atmosphere about a copper-zinc pair by means of 

 phosphoric anhydride in one instance reduced the difference of 

 potential in 173 dajs from "66 to '5 Daniell. Then, on opening 

 the instrument, it rose to '67 Daniell. 



A permanent current was produced by placing the (apparently) 

 dry plates of copper and zinc in close proximity, so that their 

 films were in contact. When the plates were either brought 

 into actual metallic contact, or separated farther apart than a 

 certain distance, as stated the current ceased. This "film- 

 cell " could also be polarised by sending a current through it 

 from another battery. 



Modifying an old experiment, due to Gassiot, so as to avoid 

 any contact of dissimilar metals, it was shown that, when the 

 zinc plate of the volta condenser was joined to the zinc quadrant 

 of the electrometer and the copper of the condenser to the 

 copper of the electrometer, on altering the capacity of the con- 

 denser an alteration of the difference of potential near the 

 quadrants was produced. 



In an appendix, Mr. J. Larmor, of St. John's College, Cam- 

 bridge, points out the difficulty of explaining this last experiment 

 by any hypothesis other than that of some kind of chemical 

 action at the surface of the metals. 



November 25. — A paper by Sir Richard Owen, F. R. S., 

 was read, of which the subject was a fossil lower jaw of 

 the large extinct marsupial quadruped which the author, 

 from previous fragmentary specimens, had referred to a carni- 

 vorous pouched species of the size of a lion, to which was assigned 

 the generic name TJiyhuoko, and the probable prey of which 

 had been the larger forms of herbivorous marsupials, which, 

 with their destroyer, had become extinct. 



Several species, allied to the kangaroo, but equalling respect- 

 ively in bulk a rhinocero--, an ox, an ass, had become extinct. 

 I'hc largest existing kind, to be seen in the Zoological Gardens, 

 was named by Dr. Shaw, Macropus major. It has escaped 

 extinction by its swiftness and power of concealment in the 

 " scrub." Wombats, also, of the size of fallow-deer, co-existed 

 with the huge kangaroos ; the small kinds, capable of concealing 

 themselves in burrows, alone survive. 



Remains of the large extinct marsupials, both devourers and 

 prey, are to be seen in the Geological Department of the 

 -Museum of Natural History ; they are described and figured in 

 the author's work on " Fossil Marsupialia." Their extinction 

 is attributed, with that of the wolf-like Cynocephalus and the 

 Thyla.olco, to the aboriginal natives of Australia. 



Linnean Society, November 18.— W. Carruthers, F.R.S., 

 President, in the chair.— Mr. H. Bury was elected a Fellow of the 

 Society.— Mr. W. H. Beeby showed specimens ol CaWtriche 

 liKiuala, Gussone, from near Westerham, Kent. The species had 



longbeen supposed to be extinct in this country, being only known 

 as British from dried specimens from Sussex in Borrer's Herba- 

 rium. — Mr. D. Morris exhibited two enlarged photographs of 

 the Castilloa Rubber-tree of Central America (see Trans, f.iiin. 

 Soc. Botany, 2nd ser. vol. ii. part 9). The larger photograph 

 illustrated the manner in wliich trees were treated to extract 

 rubber, by a special cut from above downwards. Trees of ten 

 years old and upward are said to yield about eight gallons of 

 milk at the first bleeding. This milk is coagulated by the use of 

 the juice of Calonic/yon spcciosiiiii, and the rubber prepared by 

 washing and pressing. Mr. Morris described the habit and 

 growth of the trees in their native forests, and expressed the 

 opinion that for cultural purposes this rubber-tree may be better 

 suited to the circums'ances of planters than any other. It could 

 be utilised as a sh.ide tree in cacao and coffee plantations, and 

 yield at the end of ten years at the rate of twenty shillings per 

 tree in marketable rubber. In British Honduras trees are tapped 

 for rubber every three or four years. — Mr. A. D. Michael ex- 

 hibited living specimens and preparations of an Ars^a^, received 

 from Mrs. Crawford, the State Entomologist of Adelaide. 

 Australia. The insects in question appear to be identical witli 

 the much-dreaded Argas persicws, Fischer, the bite of which was 

 supposed to cause madness and death. — Mr. H. N. Ridley made 

 remarks on specimens in spirit and drawings of species of 

 Coryanthes, viz. C. macrantha. Hook., and C. iiiactdata punctiUa . 

 He mentioned that Mr. Rodway, of Demerara, had lately pub- 

 lished observations showing that the statement of Criiger, hitherto 

 believed, as to the fertilisation by bees, did not obtain in all the 

 species ; inasmuch as in C. speciosa he (Mr. Rodway) had noticed 

 that a kind of green fly was the fertiliser. — Mr. Geo. Murray 

 exhibited specimens of Rhipilia in spirit from Grenada, West 

 Indies, obtained at a depth of five fathoms. — Mr. W. Fawcett, 

 exhibited coloured drawings of Hydtwra abyssitiica and //. 

 bogosettsis, sent by Signor Beccari from Florence. They clearly 

 showed the difference between the two species, in colour, and in 

 the former having a book-like process below the apex, and its 

 ramentiferous surfaces have long ramenta at their margins. 

 Both species differ from H. africana in the ramentiferous sur- 

 faces not extending to the apex. — Mr. C. T. Musson drew 

 attention to a branch of a blackthorn, obtained near Newark, 

 showing a curious malformation of the branchlets. — Dr. 

 Maxwell Masters read a paper on the peculiar conforma- 

 tion of the flowers of Cypripedium. The explanation may be 

 sought in the course of development, in the minute anatomy and 

 arrangement of the fibro- vascular bundles, and in the examination 

 of the comparative morphology of the flower ; organogeny affords 

 in this case only doubtful testimony, as the flower is 'irregular 

 from the first. The distribution of the primary fibro-vascular 

 bundles, and of the offshoots from them, affords more conclusive 

 evidence of the true construction of the flower, and if studied in 

 conjunction with the comparative morphology leads to very 

 satisfactory results. By these means it becomes easy to refer the 

 flower to the ordinary type seen in a regular pentacyclic and 

 trimerous monocotyledon, and from which it is reasonable to 

 infer it may have originated. The deviations from the type 

 have arisen from concrescence or inseparation of some parts, 

 inordinate development of others, and complete suppression of a 

 third series. The author cited instances showing numerous 

 intermediate gradations between the ordinary conformation of 

 Cypripedium and that of the ideal type trees, proving that what 

 was, at first, a matter of speculation and inference from imperfect 

 evidence, was borne out by actual facts. The illustrations 

 brought forward afforded examples of the reduction of parts and 

 the increased number of parts, in connection with which the 

 author alluded to the special tendency to develop the second or 

 inner row of stamens, as happens in Restiacea; and Xyridaceae, 

 while in IridaceEe the opposite tendency is manifested. Another 

 series of illustrations comprised cases of regular and of irregular 

 Piloria, which were of special importance as affording evidence 

 on the one hand of the probable past conformation of the flower, 

 and on the other of the probable course of development in the 

 future. — The fifth and concluding part of the Rev. A. Eaton's 

 monograph of recent Ephemeridae or may- flies was read. The 

 author says 55 genera and 270 species have been characterised, 

 in addition to 11 nymphs and 19 species of doubtful position ; 

 5 genera and 68 species are new to science. — Mr. J. G. Baker 

 read a paper entitled " Further Contributions to the Flora of 

 Madagascar," in which upwards of 250 new plants, seven of them 

 new genera, gathered recently by the Rev. R. Baron, F.L.S., are 

 described. Of the new genera, one belongs to Menispermacea:', 

 one to Geraniacere near Impaticns, one to Rubiacea;, and two 



