April 2. 1896] 



NA TURE 



527 



in a state of incandescence by an insulated battery, is used, then 

 a current can be obtained between this filament and both the 

 positive and negative leads. If the voltage on the lamp is raised 

 (.onsiderably above that required to give one candle-power for 

 four watts, then a current can be passed from the plate to the 

 negative lead, while a galvanometer connected to the positive lead 

 and the plate will indicate the passage of a current from the 

 ]iositive lead to the plate. When the lamp is in this condition, 

 the space between the plate and the negative lead is very sensi- 

 tive to the effects of a transverse magnetic field, such a magnetic 

 field causing a large increase in the resistance. The curve show- 

 ing the connection between the current passing from the posi- 

 tive lead to the plate and thfe volts between the terminals of the 

 lamp is found to be discontinuous. As the volts are raised the 

 current suddenly increases about ten-fold, and it is while the lamp 

 is in the condition corresponding to this upper portion of the 

 carve that it is sensitive to the influence of the transverse mag- 

 netic field. By using a movable plate it has been found that 

 the minimum current is obtained when the plate is nearer the 

 positive than the negative lead. When an alternating current 

 is used to supply the lamp, a continuous current can be obtained 

 passing from the plate to either of the leads. If a small platinum 

 cylinder is placed surrounding each of the leads, then a current 



an be obtained between each of the cylinders and the 

 iM.sitive lead, but no current between the two cylinders. 

 The largest eff'ect occurs when a cylinder near the end 

 ■ f the negative lead is connected to the positive lead. 

 The author considers that his experiments show that the resist- 

 ince of a vacuum tube to the passage of a discharge would be 

 L^reatly reduced if the kathode were made incandescent. Prof. S. 

 I'. Thompson said he would like to have some information as to 

 the state of exhaustion of the lamps ; whether this was such as is 

 found in ordinary commercial lamps, or whether it more nearly 

 approached that used by Crookes. A great change in the con- 

 ductivity, iv:c., took place at an exhaustion slightly greater than 

 that ordinarily found in incandescent lamps. It would be of 

 interest to vary the size of the kathode and to investigate 

 whether the magnitude of the effects observed depended on the 

 fall of potential per unit length along the filament. Another 

 point was whether the position of the plate, for which the effect 

 vas a minimum, was the same for all lamps, or whether it 



hanged with the volts and the length of the filament employed. 

 Again, did the minimum occur at a certain fraction of the dis- 

 tance between the positive and negative leads, or, as was the 

 case in some of the phenomena observed by Crookes, at a 

 definite distance from either of the leads. These points might 

 he investigated by means of a lamp with a straight filament 

 where the fall of potential per unit length along the filament 

 might be the same as with the loop-shaped filament, but the 

 fall of potential per unit length in the vacuum would be 

 different. The author's proposed experiment of heating the 

 kathode by concentrating on it the rays of a lamp, did not seem 



> him (Prof. Thompson) to differ materially from Crookes' 



\periment in which an incandescent wire, heated by a current,, 

 was used as the kathode. Mr. Skinner said that the heating of the 

 kathode by means of a "burning-glass" could easily be carried 

 out. Mr. Blakesley pointed out that it would be quite possible to 

 produce an increase of the current by means of a magnet. Mr. 

 Serle said that Prof J.J. Thomson had shown that a magnet 

 affected the conductivityof a gas. Prof. Fleming, in his reply, said 

 that no doubt the eff'ects were largely dependent on the vacuum 

 in the lamps. The lamps employed were exhausted to the ordinary 

 commercial vacuum. Since it was found that the "treating" 

 was more worn off" the negative leg of the filament, and that a 

 screen placed between the legs of the filament was more 

 l)lackened on the side turned towards the negative leg, it would 

 I ppear that the particles of carbon were shot off" from the nega- 



ive leg, and hei ye perhaps the charge was carried by these 

 I arbon m olecules. Ar A paper ot a purely mathematical character, 

 entitled ''j^otesontheelectromagnetic eff'ect of movingcharges," 

 by Mr. W. E. Morton, was read by Mr. Serle, who also made some 

 remarks on his own investigations dealing with this subject. 

 The Society then adjourned till April 24. 



Geological Society, March 11.— Dr. Henry Hicks, F.R.S., 

 President, in the chair.— On an Alpine nickel-bearing serpentine 

 with fulgurites, by Miss E. Aston, with pctrographical notes by 

 Prof. T. G. Bonney., F.R.S. The specimens described were 

 collected on the summit of the Riff"elhorn (near Zermatt) by Prof. 

 W. Ramsay, F.R.S. , and Mr. J. Eccles, and they showed some 

 ver)' well-marked " lightning-tubes." The rock was a serpentine, 



NO. 1379, VOL. 53] 



somewhat schistose from pressure, which had been formed by the 

 alteration of a rock chiefly composed of olivine and augite. One 

 of the analyses gave 4-92 per cent, of nickel oxide and hardly 

 any lime. Prof Bonney detected some awaruite under the 

 microscope, but not nearly enough to account for the analysis. 

 Reasons were given to show that the nickel oxide prolxibly 

 replaced lime in the pyroxenic constituent of the rock. The 

 tubes, about yV inch in diameter, were round in .section, cleanly 

 drilled, and lined with a very thin film of dark brown or black 

 glass. — The Pliocene glaciation, preglacial valleys, and lake- 

 basins of subalpine Switzerland : with a note on the microscopic 

 structure of Tavayanaz diabasic tufa, by Dr. C. S. Du Riche 

 Preller. The main object of this paper, which was the sequel to 

 one read last session, was to solve the problem whether the 

 Pliocene glacio-fluviatile conglomerates of the Swiss lowlands 

 were deposited on a plateau or in already existing valleys. For 

 the purpose of this inquiry, the author examined last summer 

 a large additional number of glacial high- and low-level deposits 

 throughout the Zurich Valley over an area more than 40 miles 

 in length ; and his investigations further led him to important 

 conclusions with respect to the combination of causes which 

 determined the formation of the lake basins lying in the same 

 zone at the foot of the Alps. He showed that the Lake of 

 Zurich owes its origin, in the first instance, to a zonal subsidence 

 (probably between the first and second glaciation) of about lOOO 

 feet, as evidenced by the reversed dip of the disturbed molasse- 

 strata between the lakes of Zurich and Zug. During the second 

 and third Ice-periods, the original lake-basin was gradually filled 

 with glacial and fluviatile deposits at both ends, and was finally 

 restricted to its present dimensions by a post-glacial bar deposited 

 at its lower end by a tributary river. In the author's view, the 

 other subalpine lakes, extending from the Lake of Constance to 

 Lac Bourget in Savoy, owe their origin and present limits, in 

 the main, to the operation of similar causes. With regard to 

 the main question, he averred that the Lower and Middle Pliocene 

 period was, in Switzerland, entirely one of erosion and denuda- 

 tion on a prodigious scale. Irre.spective of the evidence he had 

 adduced, he was therefore driven to the conclusion that at the 

 advent of the first Ice-period in Upper Pliocene times the 

 principal subalpine valleys must have been already excavated 

 approximately to their present depth, and that ever since then 

 the action of the great Alpine and subalpine rivers had been, as 

 it is still in our own day, mainly directed to regaining the old 

 valley-floors by removing those enormous accumulations of 

 glacial and glacio-fluviatile material, which are respectively the 

 direct and indirect products of three successive and general 

 glaciations. — Notes concerning certain linear marks in a 

 sedimentary rock, by Prof. J. E. Talmage. The marks described 

 in the paper occur in a fine-grained argillaceous sand.stone 

 referred by the U.S. Geological Survey to the Triassic or Jura- 

 Trias period, which is found on a low tableland within two miles 

 of the bluffs overlooking Glen Canyon. The marks commonly 

 appear as straight lines intersecting at right angles, but .some 

 have a pinnate distribution, suggesting engravings of frost- 

 flowers. A description of the markings was given, and various 

 experiments made m the laboratory to illustrate the effects of 

 formation of crystals formed over sediment were de.scribed. 



Paris. 



Academy of Sciences, March 23. — M. A. Cornu in the 

 chair. — On the invisible radiations emitted by the .salts of 

 uranium, by M. II. Becquerel. A confirmation and extension 

 of previous experiments upon potassium uranyl sulphate. 

 Uranium salts appear to be unique in the length of time during 

 which they give off photographically active rays in the dark. On 

 comparing the rate of discharge of a gold leaf electroscope by the 

 radiations from a crystal of potassium-uranyl sulphate and a 

 Crookes' tube respectively, the efTecl of the tube was found to 

 be over one hundred times greater than that of the crystal. — 

 Observations on the preceding communication, by M. L. Troost. 

 — Observations relating to a note of M. C. Henry, entitled " On 

 the principle of an accumulator of light," by M. H. Becquerel. 

 An account of some earlier work on the .same subject over- 

 looked by M. Henry. — Application of the X-rays to the diagnosis 

 of surgical diseases, by M. Lannelongue. A description of the 

 results obtained in two cases, in the second of which a suppo.sed 

 exostosis was shown not to exist, the pain and inu.scular atrophy 

 iieing due to hysteria. — Researches on the earths contained in 

 the monazite sands, by MM. P. Schiitzenberger and O. 

 Boudouard. — On the quantities of nitric acid contained. 



