April 



1893] 



NATURE 



599 



spores, and have compared these with the trabeculse in the 

 sporangium of Isoetcs. Neither of these sporangia are, however, 

 completely partitioned. I now suggest that comparatively slight 

 modification of the condition in Lepidodendron would produce 

 the state of things seen in Tmesipteris : if the sterile trabeculse 

 of Lepidodendron were consolidated into a transverse septum, 

 and the apical growth of the sporophyll 'arrested and taken up 

 by two lateral lobes, the result would be such as is seen in 

 Tmesipteris. This is not a mere imaginative suggestion : it pro- 

 ceeds from the observed fact that the septum in Tmesipteris is 

 indistinguishable at first from the sporogenous masses. It may 

 further be noted, in connection with the above comparison 

 between Lepidodendron and Tmesipteris, that the vascular tissues 

 of some of the former appear to correspond more closely to those 

 of Tmesipteris than to any other living plant. 



Looking at the whole plants of the Psilotaceae from the point 

 of view 5ibove indicated, ihey are to he regarded as lax strobili, 

 bearing sporangiophores (sporophylls) of rather complex struc- 

 ture. Branching, which is rare in Tmesipteris, is common in 

 Psilotum, and is to be compared with the branching of the 

 strobilus in many species of Lycopodiwn. In both there are 

 irregularly alternating sterile and fertile zones, not unlike those 

 of some species of Lycopodium ; at the limits of these arrested 

 sporangia are frequently found. It is not difficult to imagine 

 how such plants as the Psilotaceas may have originated from 

 some strobiloid type, not unlike that of the genus Lycopodium. 



March 23. — "The Absolute Thermal Conductivities of 

 Copper and Iron." By R. Wallace Stewart, B.Sc. (London), 

 Assistant Lecturer and Demonstrator in Physics, University 

 College, Bangor. Communicated by Lord Kelvin, P. R.S. 



The experiments described in the paper were undertaken 

 with the object of determining the thermal conductivity at 

 different temperatures of iron, and, in particular, of pure, elec- 

 trolytically deposited copper. 



The method adopted was that due to Forbes, but the thermo- 

 electric method of deteraiining temperature was employed, and 

 the bar was protected from currents of air and external radiation 

 by surrounding it by a trough of sheet zinc. 



The iron bar used was a square ^-inch barof ordinary wrought 

 iron ; the copper bar was a round ^inch bar of pure electrolytic 

 copper. 



The variation of the specific heat of iron with the tempera- 

 ture was determined by Bunsen's calorimeter ; for the specific 

 heat of copper the result given by Bede was taken. 



The range of temperature over which the observations ex- 

 tended was from 15° C. to about 220° C. 



The final results obtained are indicated by the formulas given 

 below, and tend to show that for both copper and iron the con- 

 ductivity decreases with rise of temperature. 



Results for Lron in C.G.S. Units. 



DifTusivity, k, at t° C. is given by — 



«-/ = 0"2o8 (1-0-03175/), 

 and the absolute thermal conductivity, k, by — 

 /(v=o-i72 (I -0001 1/). 



Results for Copper in C.G.S. Units. 

 DifTusivity, k, at t° C. is given by — 



I. ic^= I -370 (i -000125/). 



II. «;= 1-391 (l -0*00I20/). 



The mean of these results is taken as — 

 Ki=i-i2> (i -0-0012/), 

 and the value of the absolute conductivity, k, is then given by — 

 >^;=i-io (i -0-00053/). 



A table is given at the end of the paper showing the emissive 

 power of the surface of each bar at temperatures between 20° C. 

 and 200° C. 



Linnean Society, April 6. — Prof. Stewart, President, in 

 the chair. — The President took occasion to refer to the great 

 loss which botanical science had sustained by the death, on 

 April 4, of Prof. Alphonse de Candolle of Geneva, an announce- 

 ment which was received with profound regret. Prof, de Candolle 

 was the senior foreign member of this Society, having been 

 elected in May 1850, and was the recipient of the Society's Gold 

 Medal in 1889. — Mr. Clement Reid exhibited and made some 

 remarks upon the fruit of a South European Maple [Acer 

 monspessiilanum') from an interglacial deposit on the Hampshire 

 coast. — Mr. R Lloyd Prreger, who was present as a visitor, 



NO. 1225, VOL. 47] 



exhibited some rare British plants from the co. Armagh, and 

 gave an account of their local distribution. — A paper was then 

 read by Mr. W. B. Hemsley on a collection of plants from the 

 region of Lhassa, made by Surgeon-Captain Thorold in 1891, 

 and a further collection from the Kuenlun plains made hy 

 Captain Picot in 1892. Some of the more interesting plants 

 were exhibited, and critical remarks were offered by Messrs. 

 C. B. Clarke, J. G. Baker, and Dr. Stapf.— Dr. H. C. Sorby 

 gave a demonstration with the oxyhydrogen lantern and 

 exhibited a number of slides which he had prepared of small 

 marine organisms, many of them extremely beautiful, mounted 

 transparently so as to show the internal structure. 



Entomological Society, April 12. — Mr. Frederic Merrifield, 

 Vice-President, in the chair. — Sir John T. Dillwyn Llewelyn, 

 Bart., exhibited a number of specimens of Lepidoptera, Coleop- 

 tera, And Hymenoptera, all caught in Glamorganshire. The 

 Lepidoptera included two remarkable varieties of Vanessa io, 

 both obtained from the same brood of larvae from which 

 the usual eye like spots in the hind wings were absent ; 

 varieties of Arctia menthastri ; a long series of melanic 

 and other forms of Boarmia repandaia and Tephrosia crepus 

 cnlaria ; and bleached forms of Geometra papilionaria. The 

 Coleoptera included specimens of Prionus coriarius, Pyrochroa 

 coceinea, Otiorhynchus sulcatus, and Astynomus cedilis, a large 

 species of Longicornia, which Sir John Llewelyn stated had 

 been handed to him by colliers, who obtained them from the 

 wooden props used in the coal mines, made out of timber im- 

 ported from the Baltic. Mr. Merrifield, Dr. Sharp, F.R.S., 

 and Mr. Stevens made some remarks on the specimens. — Sir 

 John T. D. Llewelyn inquired whether the name of the moth 

 which had a sufficiently long proboscis to fertilise the large 

 Madagascan species of Orchis, Aiignzictim sesquipedale, was 

 known. Mr. C. O. Waterhouse stated that the collections 

 received at the British Museum from Madagascar had been ex- 

 amined with the view to the discovery of the species, but up to 

 the present it had not been identified. — Mr. H. Goss exhibited, 

 for Mr. Frank W. P. Dennis, of Bahia, Brazil, several nests of 

 Trap-door Spiders, containing living specimens of the spider, 

 and read a communication from Mr. Dennis on the subject. 

 Several photographs of the nests and the spiders were also ex- 

 hibited. It was stated that Mr. Dennis had found these nests 

 at Bahia in one spot only in a cocoa-nut grove close by the sea. 

 — Mr. McLachlan, F. R S., read a paper entitled "On species 

 of Chrysopa observed in the Eastern Pyrenees ; together with 

 descriptions of, and notes on, new or little-known Palasarctic 

 forms of the genus." The author stated that the species referred 

 to in this paper had been observed by him in the Eastern 

 Pyrenees, in July, 1886, when staying with Mons. Rene 

 Oberthiir. After describing the nature of the district, and its 

 capabilities from an entomological point of view, the paper 

 concluded with descriptions of certain new palasarctic species of 

 the genus. Dr. Sharp, who said that he was acquainted with 

 the district, and Mr. Merrifield made some remarks on the paper. 



Paris. 

 Academy of Sciences, April 10. — M. Loewy in the chair. 

 — The deaths were announced of Vice-Amiral Paris and M. 

 Alphonse de Candolle. — On the extinction of torrents and the 

 replanting of the highlands, by M. P. Demontzey. A report 

 on the work done since 1883 towards securing the south of 

 France from its periodical inundation by mountain torrents. — 

 On the, loss of electric charge in diffused light and in darkne'^s, 

 by M. Edouard Branly. — Dynamo-electric machinery with com- 

 pound excitation, by M. Paul Hoho. If a curve be con- 

 structed showing how the magnetic excitation of a dynamo- 

 electric machine ought to vary in order that the E.M.F. may 

 remain constant, or may vary according to a given law, it is 

 possible to contrive an excitation such that, if it be also ex- 

 pressed by a curve, the latter will cut the former in any num- 

 ber of points required. Between these paints of intersection 

 the two curves nearly coincide. Hence it is possible to pro- 

 duce currents which, between certain limits, do not vary with 

 the speed of the engine. This has been practically realised 

 by means of two separate exciter circuits. — On anomalous 

 dispersion, by M. Salvator Bloch. — General conditions to be 

 fulfilled by registering instruments or indicators ; problem of 

 integral synchronisation, by M. A. Blondel. All the instru- 

 ments in question consist essentially of a movable piece (needle, 

 pencil, membrane, or mirror) susceptible of rectilinear or 

 circular displacement under the simultaneous influence of a 



