February 3. 1898] 



NA TURE 



335 



ment-circuit, and finally to the *' tapping-back " apparatus. A 

 coherer is more sensitive when thus isolated and exposed to the 

 full influence of the received oscillations ; the subsequent detec- 

 tion of the effect by altered connections is very convenient for 

 laboratory measurements. A diagram of a series of plotted 

 measurements showed that the resistance of an undisturbed 

 filings-tube is approximately a direct function of the intensity of 

 the received stimulus, whether successive stimuli increased or 

 decreased in strength. This electrical process of " tapping- 

 liack " is to be depended upon, but the process long continued 

 fatigues the tube until a mechanical shake is employed to restore 

 it. Large size apparatus made by Dr. Muirhead for actual dis- 

 tant syntonic work was exhibited, and means were shown 

 for protecting and isolating the coherer when its receiving 

 areas were being used as emitters ; also a switch used 

 for changing at one moment all the connections from 

 "sending" to "receiving." Prof. Threlfall said he had come 

 to the same conclusion as Prof. Lodge as to the advisability of 

 diminishing the number of contact-points in the coherer. He 

 had endeavoured to produce longer and more persistent waves, 

 and thus to set afield greater effective energy. It was desirable 

 to keep the waves as parallel as possible. He thought there was 

 some probability that the wave-fronts could be altered and 

 rendered more conformable by a process of diffraction. Mr. 

 Rutherford also had found it best to work with long waves. He 

 fully appreciated the advantage of increasing the capacity of the 

 oscillator by extending the surface of the metallic plates. Mr. 

 Campbell-Swinton asked whether experiments had been made 

 to verify Hertz results as to the influence of reflectors behind 

 oscillators and receivers. He had found them disadvantageous. 

 A single wire behind either apparatus seemed partially to annul 

 the effect. He also asked whether Prof. Lodge had observed 

 the extraordinary sensitiveness of coherers to small changes of 

 current in neighbouring circuits. Prof. Lodge, in reply, said he 

 had observed the sensitiveness to slight sudden variations of 

 current referred to by Mr. Campbell Swinton; for instance, 

 when electric lamps were switched on or off. The effect of 

 mirrors had been studied by Prof. Fitzgerald. They required 

 to be of large dimensions as compared to the oscillator and 

 receiver, otherwise the true reflections were not obtained. Dr. 

 Silvanus Thompson afterwards exhibited a Tesla oscillator. 

 This apparatus is intended to replace the two induction coils 

 and spark-gap arrangements used by Mr. Tesla for high fre- 

 quency experiments. It consists of an induction coil with a 

 separate self-inductance coil in the primary circuit. This self- 

 inductance coil is also used as an electromagnet for the separate 

 interrupter of the primary circuit. A condenser is connected 

 between one end of the primary coil and one terminal of the in- 

 terrupter, so as to include both of them between its terminals. 

 The primary is a single turn of copper strip, six inches 

 wide. The secondary is one layer of thick wire ; each turn 

 separated from the next by an air space. The supply current, 

 about half an ampere, may be taken from the electric-light 

 mains at almost any voltage from 50 to 200, direct or alternat- 

 ing. Prof. L(xlge said it would work quite well at 10 volts. 

 He pointed out also that if the straight discharge-rods at the 

 spark-gap were free to slide, the discharge drove them back 

 into their sockets. Prof. Fitzgerald said it was stated at 

 Toronto that the spark was broken at the interrupter when the 

 condenser was charged, and that by the time the condenser was 

 ready to discharge, the contact at the interrupter had been made 

 again. It seemed to him that the condenser discharges and 

 surgings must take place at a rate far higher than the period of 

 the mechanical movement of the interrupter. The condenser 

 charges and discharges were very rapid. It was not what is 

 ordinarily called the "time constant" that was involved, for 

 that only referred to constant voltage. Here the voltage was 

 changing very rapidly indeed. Prof Herschel asked if such an 

 apparatus was suitable for work with Rontgen rays. Dr. 

 Thompson, in reply, congratulated Mr. Tesla upon the perfect 

 working and compactness of his invention. The present form 

 was not suited for Rontgen ray experiments, but Mr, Tesla 

 had designed a special coil that was excellent for that purpose. 

 — The President proposed votes of thanks, and the meeting 

 was adjourned until February 11. 



Paris. 

 Academy of Sciences, January 24.— M. Wolf in the chair. 

 — On the reduction of some double integrals, and on a new in- 

 variant in the theory of algebraic surfaces, by M. ^mile Picard. — 



NO. i475» VOL. 57] 



Addition to a preceding note on the Zeeman effect, by M. .-V 

 Cornu. Some results of measurements showing that the magni- 

 tude of the separation produced increases with the refrangibility of 

 the ray. — On the conditions of formation of alkaline carbides, 

 and the carbides of magnesium and of the alkaline earths, by 

 M. Henri Moissan. Metallic potassium, if left for a long time 

 in acetylene, slowly but completely decomposes the gas giving 

 hydrogen and CjHK. Sodium gives a similar compound when 

 sealed up with liquid acetylene, and this CjHNa, heated in a 

 vacuum, gives up pure acetylene, leaving sodium carbide C.jNa« 

 behind ; at a red heat this is decomposed into carbon and 

 sodium. The potassium compound behaves similarly, neither 

 sodium, potassium, nor magnesium carbides being able to exist 

 at the temperature of the electric furnace. — Histological 

 mechanism of cicatrisation ; on true immediate reunion, by 

 M. L. Ranvier. In wounds caused by cutting the cornea of 

 the rabbit, two modes of closing up of the tissue can be noted, 

 an immediate synaptic joining, and a true immediate joining, 

 the former due to the cuts being filled with epithelial cells 

 arising from the neighbouring epithelium, and the latter notice- 

 able only in wounds forty-eight hours after the incision had 

 been made, and where, owing to the lips of the cut happening 

 to touch, no epithelial cells had penetrated. — The enlargement 

 of the right auricle of the heart during inspiration demonstrated 

 by radioscopy, by M. Ch. Bouchard. — On the fourth voyage of 

 the Princesse-AHce, by S.A.S. Albert I., Prince of Monaco. 

 The chief work was done on the western coast of Morocco, 

 round Madeira and the .'\zores, and comprised sounding oper- 

 ations, together with zoological study of the fauna of the 

 Princesse- Alice bank. A chart of this bank accompanies the 

 paper. — Remarks by M. Edmond Perrier on his work on 

 animal colonies and the formation of organisms. —Shooting- 

 stars in the months of November and December 1897, ob- 

 served at Basse-Terre (Guadeloupe), by M. Ch. Duprat.— On 

 the development of uniform or holomorphic functions in 

 any field, by M. Paul Painleve. — On the types of increase 

 and on complete functions, by M. Emile Borel. — On systems 

 of partial differential equations analogous to equations 

 of the first order, by M. Jules Beudon. — On the geometry 

 of magnetic fields and of motion with two degrees of freedom 

 in a plane or on a sphere, by M. Rene de Saussure. — Law of 

 deformation of commercial metals, by M. Marcel Brillouin. A 

 mathematical expression is given which includes all the known 

 facts regarding permanent changes of shape in metals. — On an 

 interference spectroscope, by MM. Ch. Fabry and A. Perot. 

 The method consists in observing rings produced by trans- 

 mission through a layer of air contained between two perfectly 

 parallel silvered glass faces. Full details of the adjustments 

 necessary are given in the present paper. — On the part played 

 by diffraction in the effects produced with gratings, by M. Ch. 

 Fery. — Study of chemical and physical equilibria by the osmotic 

 method, by M. A. Ponsot. — On the law of mixture of gases, by 

 M. Paul Sacerdote, giving the experimental results of mixing 

 equal volumes of gases. The observed changes of pressure for 

 a mixture of nitrous oxide and carbon dioxide, and of the latter 

 gas \yith sulphur dioxide, are compared with those deduced 

 from the densities by M. Leduc. The results of the two methods 

 are in general agreement. — On the separation of thorium and 

 the cerite earths, by MM. G. Wyrouboff and A. Verneuil. — 

 The method proposed is based upon the fact that in a mixture of 

 nitrates of the rare earths, as free as possible from excess of acid, 

 heating with excess of hydrogen peroxide to 60" completely 

 precipitates all the thoria in the solution. — Hydramides and the 

 isomeric glyoxalidines, by M. Marcel Delepine. A thermo- 

 chemical paper.— Researches on ouabaine, by M. Arnaud. — 

 Synthesis of terebic acid, by M. E. E. Blaise. —Manufacture of 

 acetone oil, in particular of methyl-ethyl-ketone. by means of 

 the liquors from the desuintage of wool, by MM. A. and P. 

 Buisine. The calcium salts of the mixture of fatty acids obt lined 

 from wool is submitted to dry distillation. The resulting liquid 

 yields on fractionation 60 per cent, of methyl-ethyl ketone. 

 — On the estimation of gastric juice, by M L. Cordier. The 

 free acid is converted into lithium chloride by treatment with 

 lithium carbonate, and this separated from the sodium chloride 

 by extracting the incinerated residue with a mixture of equal 

 parts of absolute alcohol and dry ether, in which the lithium 

 chloride only is soluble. — Ergographical experiments for measur- 

 ing the maximum power of a muscle regularly stretched, by 

 MM. Andre Broca and Charles Richet. — The fungus Sporo- 

 trichum globuliferum , by M. Trabut. — On the anhydrous cal- 



