May 2! 



NA TURE 



93 



ference to Table III. shows that a considerable amount of 

 E.M. F. was developed between the various metals in every 

 instance, which is a circumstance of much interest in connection 

 with the passive state of iron and steel. 



(5) The results obtained in Part III., Series V. and VI., on 

 the relative passivity of wrought-iron and the various steels — 

 soft cast-steel, hard cast-steel, soft Bessemer steel, hard Bes- 

 semer steel, soft Siemens steel, and hard Siemens steel — are of 

 an important character, showing, by the delicate electro-chemical 

 method employed, the sensitive influence of difference in che- 

 mical composition and physical structure, &c., on the passive 

 state of the metals. Generally throughout this series of experi- 

 ments it will be observed that the wrought-iron was electro- 

 positive to the steels with a considerable E. M.F., amounting, 

 in some cases, to as high as one tenth to one-seventh of a volt, 

 the wrought-iron being thus shown to be less passive than the 

 steels. 



A reference to the experiments on the wrought-iron and various 

 steel plates, on Table VIII., shows that the E.M.F. between 

 the passive wrouglit-iron and the various soft steels, which con- 

 tained less percentage of combined carbon, in circuit in cold 

 nitric acid, sp. gr. i 42, was very considerably less than the 

 E.M.F. under similar conditions between the wrought-iron 

 plates and the different hard steels having a higher percentage of 

 combined carbon. The latter results, therefore, demonstrate 

 the interesting circumstance that steels of a higher percentage 

 of combined carbon are more passive than those of a lower per- 

 centage of combined carbon. It will be observed that the 

 wrought-iron was also electro-positive to most of the steels, 

 whether of a higher or lower percentage of combined carbon, 

 which shows that wrought-iron may be regarded as generally 

 less passive than steels. 



May 14. — " Researches on the Structure, Organization, and 

 Classification of the Fossil Reptilia. VII, Further Observa- 

 tions on Pareiasaurus." By H. G. Seeley, F.R.S., Professor 

 of Geography in King's College, London. 



All the affinities hitherto attributed to Pareiasaurus with 

 Labyrinthodonts, Anomodonts, Procolophon, and Mammals are 

 shown more strongly in the several parts of the skeleton, by the 

 new evidence. The shoulder-girdle is more Labyrinthodont 

 than was previously supposed, the skull is more Reptilian, and 

 the pelvis and limbs are more Mammalian, though with some 

 resemblance to Dinosaurs. 



From furthur evidence of the structure of the skeleton in 

 Procolophott, the author regards that type as a member of the 

 Pareiasauria, rather than as forming a distinct sub-order. It 

 also has four sacral vertebras. 



The divisions of the Anomodontia are grouped as — 



Theriodontia. 



/ \ 



Placodontia. Dicynodontia. 



IEndothiodontia. 

 / \ 



Pareiasauria. Mesosauria. 



Physical Society, May 9. — The Society varied its ordinary 

 procedure by paying a visit to the ancient seat of learning 

 situated on the banks of the Cam. Assembling at Liverpool 

 Street Station, members and visitors to the number of about 

 one hundred were conveyed in saloon carriages by the il 

 o'clock express direct to their destination, the whole journey 

 being accomplished in about seventy-five minutes. Amongst 

 those present were Dr. E. Atkinson, Prof. Ayrton and Mrs. 

 Ayrton, Mr. Walter Baily, Mr. Sbelford Bidwell and Mrs. Bid- 

 well, Mr. D. J. Blaikley, Mr. T. H. Blakesley and Mrs. Blakes- 

 ley, Mr. J. T. Bottomley, Mr. C. V. Boys, Prof. Carey Foster, 

 Mr. Conrad W. Cooke, Prof. Fitzgerald, Dr. E. Frankland and 

 Mrs. Frankland, Dr. W. R. Hodgkinson, Prof. O. J. Lodge, 

 Prof. Meldola, Prof. Perry and Mrs. Perry, Prof. Riicker, Dr. 

 Sumpner, Prof, S. P, Thompson and Mrs. Thompson, Mr, A. P. 

 Trotter and Mrs. Trotter, and Mr, G. M. Whipple. On arriving 

 at the historic town the party became the guests of the Cam- 

 bridge members, and proceeded to Emmanuel College, where 

 they were received by Mr. W, N, Shaw. Various groups 

 visited the cloisters, chapel, and gardens, and at one o'clock 

 lunch was provided in the College Hall. At 2.30, a meet- 

 ing of the Society was held in the Lecture Room of the Caven- 

 dish Laboratory. The papers read were all by authors resident 



in Cambridge, and the abstracts given below will sufficiently 

 indicate the variety of the subjects brought before the Society. 

 After the meeting the visitors inspected the Cavendish Labora- 

 tory. Amongst the many interesting instruments and apparatus 

 to be seen, specially noticeable were Prof. J. J. Thomson's 

 50-feet vacuum tube, glowing from end to end with a luminous 

 discharge; Mr. Shaw's pneumatic bridge, by which the pneumatic 

 resistance or conductivity of various shaped orifices and channels 

 can be compared ; and the new air condensers to be used by 

 Mr, Glazebrook as standards. The Cambridge Scientific Instru- 

 ment Company had an interesting exhibit, including a dividing 

 engine, Boys's radio-micrometer, electrically driven tuning-forks, 

 and various recording instruments, amongst which was Galton's 

 apparatus for registering the growth of plants. Other things 

 which attracted attention were Glazebrook's spectrophotometer ; 

 Lord Rayleigh's coils and apparatus used in his determination of 

 the ohm ; a collection of models, medals, and instruments, 

 formerly belonging to Prof. Maxwell ; the resistance standards 

 of the British Association, together with the historic rotating 

 coils and electrodynamometer used in the determination of the 

 B. A. unit. Tea was served in the Combination Room of 

 Trinity College, and a majority of the visitors returned to town 

 by the 8 o'clock express, greatly pleased with the day's 

 outing. Others, however, prolonged their visit until Monday, 

 and had opportunities of discussing important physical problems 

 with the Cambridge members. The meeting was in every sense 

 a great success, and will long be remembered as a red-letter day 

 in the history of the Society. — At the science meeting, held in 

 the Cavendish Laboratory, Prof. Ayrton, F. R.S., President, in 

 the chair, the following communications were made : — Some 

 experiments on the electric discharge in vacuum tubes, by Prof. 

 J. J, Thomson, F. R. S. The phenomena of vacuum discharges 

 were, he said, greatly simplified when their path was wholly 

 gaseous, the complication of the dark space surrounding the 

 negative electrode and the stratifications so commonly observed 

 in ordinary vacuum tubes being absent. To produce discharges 

 in tubes devoid of electrodes was, however, not easy to accom- 

 plish, for the only available means of producing an electromotive 

 force in the discharge circuit was by electro-magnetic induction. 

 Ordinary methods of producing variable induction were value- 

 less, and recourse was had to the oscillatory discharge of a 

 Leyden jar, which combines the two essentials of a current whose 

 maximum value is enormous, and whose rapidity of alternation 

 is immensely great. The discharge circuits, which may take the 

 shape of bulbs or of tubes bent in the form of coils, were placed 

 in close proximity to glass tubes filled with mercury, which 

 formed the path of the oscillatory discharge. The parts thus 

 corresponded to the windings of an induction coil, the vacuum 

 tubes being the secondary and the tubes filled with mercury the 

 primary. In such an apparatus the Leyden jar need not be large, 

 and neither primary or secondary need have many turns, for 

 this would increase the self-induction of the former and lengthen 

 the discharge path in the latter. Increasing the self-induction 

 of the primary reduces the E. M. F. induced in the secondary, 

 whilst lengthening the secondary does not increase the E.M.F. 

 per unit length. Two or three turns in each were found to be 

 quite sufficient, and on discharging the Leyden jar between two 

 highly polished knobs in the primary circuit a plain uniform 

 band of light was seen to pass round the secondary. An 

 exhausted bulb containing traces of oxygen was placed within a 

 primary spiral of three turns, and on passing the jar discharge 

 a circle of light was seen within the bulb in close proximity to 

 the primary circuit, accompanied by a purplish glow which lasted 

 for a second or more. On heating the bulb, the duration of 

 the glow was greatly diminished, and it could be instantly 

 extinguished by the presence of an electro-magnet. Another 

 exhausted bulb surrounded by a primary spiral was contained 

 in a bell jar, and when the pressure of air in the jar was 

 about that of the atmosphere, the secondary discharge occurred 

 in the bulb, as is ordinarily the case. On exhausting the jar, 

 however, the luminous discharge grew fainter, and a point was 

 reached at which no secondary discharge was visible. Further 

 exhaustion of the jar caused the secondary discharge to appear 

 outside the bulb. The fact of obtaining no luminous dis- 

 charge either in the bulb or jar the author could only explain 

 on two suppositions, viz. that under the conditions then existing 

 the specific inductive capacity of the gas was very great, or that 

 a discharge could pass without being luminous. The author 

 had also observed that the conductivity of a vacuum tube with- 

 out electrodes increased as the pressure diminished, until a certain 



NO. I I 26, VOL. 44] 



