CHEMICAL NEWS, March 18, 1910 Direct Union of Carbon and Hydrogen. 125 The para-quinonoid structures respectively. Another weak | is transformed by chlorine into a very unstable neutra point in the quinone hypothesis as regards aromatic derivatives was the fact that the heteronuclear nitro-anaphthylamines (1: 5- and 1: 8-) were red, whilst the possibly quinonoid ortho- and para-nitro-a-naphthylamines were less intensely coloured. since the absorption spectra of the nitroanilines and the corresponding sodium nitrophenoxides were identical, it would be necessary to write similar formula for the latter; for example, II., and, as Dr. Hewitt had agreed that this was improbable, it followed that it was equally improbable for the nitroanilines. With regard to Mr. Buttle and Dr. Hewitt's work on picric acid and trinitroanisole, this was dealt with in the paper, where it was shown that their results were capable of a simple explanation. In reply to Dr. Lowry, he did not understand the objection to the statement that the nitro-group had a free period of absorption, because there seemed to be no doubt whatever on that point as the result of the examination of a great number of compounds. *56. "Action of Ethyl Cyanoacetate on 5-Chloro-1 : 1dimethyl-A-cyclohexen-3-one." By ARTHUR WILLIAM CROSSLEY and CHARLES GILLING. It has been shown (Trans., 1909, xcv., 27) that during the action of ethyl malonate on chlorodimethylcyclohexenone, a solid nitrogenous by-product melting at 141° is obtained, its formation being due to the fact that the ethyl malonate employed contained some ethyl cyanoacetate. When the latter substance is used instead of ethyl malonate in the above condensation, there is produced 75 per cent of the theoretical quantity of the substance melting at 141°, which has been shown by a detailed study of its properties and transformations to be ethyl hydroxydimethylcyclohexenylidenecyanoacetate, 57. "The Constitution of Carpaine." Part I. By GEORGE BARGER. Carpaine, the alkaloid from the leaves of the Papaw tree, Carica Papaya, L., was discovered by Greshoff, and has been further examined by Merck and by van Ryn (Arch. Pharm., 1897, ccxxxv., 332), who found that it is a secondary base of the formula C14H25O2N. In the present investigation it has so far been shown that carpaine is hydrolysed by acids and baryta to a substance, C14H27O3N, soluble in water, which contains a carboxyl group and is also a base. It closely resembles certain amino-acids, and the name carpamic acid is suggested for it. When heated with alcoholic hydrogen chloride, carpaine yields the hydrochloride of ethyl carpamate, C13H26ON CO2Et, HCl. The hydrochloride of carpaine substance, C14H23O3NCl2, insoluble in water and melting at 77 after crystallisation from methyl alcohol. yield of all the above substances is quantitative. On oxidation by potassium permanganate in acetone solution, a nitrogenous acid results, from which ultimately a minute quantity of a crystalline dibasic acid, C8H1404, can be obtained, probably a-dimethyladipic acid. The latter acid is also produced, in very much larger quantity, by oxidation of carpaine with nitric acid. 58. "Optically Active Glycols Derived from 1-Benzoin and from Methyl 1-Mandelate." By ALEX. MCKENZIE and HENRY WREN. The preparation of a number of optically active glycols derived from 1-benzoin and from methyl l-mandelate was described. Whilst l-benzoin and certain of its derivatives, such as the methyl ether, undergo racemisation with great ease in the presence of alkali, this racemisation is prevented when the carbonyl group in 1-benzoin is displaced by the CRR OH group. With one exception the glycols described are dextrorotatory; -triphenylethylene glycol, for example, has [a] D +2213° in acetone solution, and, since the same compound may be obtained either from l-benzoin or from methyl l-mandelate, the change of sign is probably not due to a Walden inversion. When -triphenylethylene glycol is alkylated by a mixture of methyl iodide and silver oxide, only one of the two hydroxy-groups is methylated. The monomethoxycompound obtained in this manner has the formula and has [a] + 185.3° in acetone solution. OMe CHPh CPh2 OH, and not OH CH Ph CPh2 OMe, 59. "The Colour and Constitution of Azo-compounds." Part V. By JOHN THEODORE HEWITT and FERDINAND BERNARD THOLE. The authors have isolated benzeneazobenzenediazonium salts (chloride, platinichloride, and chromate or dichromate) in a solid form. Whilst the two former salts were analysed, the salt of chromic acid proved too explosive (compare Meldola and Eynon, Trans., 1905, lxxxvii., 4). The chloride is characterised by great stability, and may be kept for months in a solid state without undergoing appreciable change, whilst its alcoholic solution does not undergo tion spectrum of this salt with those of aminoazobenzene rapid decomposition. From a comparison of the absorphydrochloride and benzeneazophenyltrimethyl-ammonium iodide, no deductions are drawn as to its constitution, but attention is drawn to this further case of stability of diazonium salts being greatly increased by negative substituents in the para-position. Iodoazobenzene in alcoholic hydrogen chloride gives an absorption spectrum which renders it probable that an sibly the compound is formed with two molecules of iodonium salt, C6H5 NH N:C6H4:I Cl, is produced. Poshydrogen chloride. 60. "The Direct Union of Carbon and Hydrogen at High Temperatures." Part II. By JOHN NORMAN PRING. In continuation of an earlier investigation (Pring and Hutton, Trans., 1906, lxxxix., 1591), the author has made a quantitative study of the reaction between carbon and hydrogen at temperatures ranging from 1100° to 2200°. The materials used were submitted to the most exhaustive purification, and the presence of moisture and nitrogen was carefully eliminated. The carbon was heated electrically, and out of all contact with any possible source of contamination. Direct union with hydrogen was found to occur at all temperatures, methane being formed below 1800°, and methane, acetylene, and ethylene above this temperature. The formation of methane reached a minimum (0.16 per cent) at about 1550°. Some experiments carried out on the decomposition of acetylene and methane showed that at 1775° the former gas changes quickly into the latter, and the methane decomposes only very slowly. At 1200°, small percentages of ROYAL SOCIETY. Ordinary Meeting, March 3rd, 1910. acetylene in an excess of hydrogen were found to change slowly into methane and ethylene. In presence of platinum, the reaction between the carbon and the hydrogen was very much accelerated, and values were obtained Sir ARCHIBALD GEIKIE, K.C.B., President, in the Chair. which, at 1200°, amounted to o'55 per cent, and at 1500 to o 30 per cent, of methane. On decomposing an excess of methane, an amount equal to 0.59 per cent of the gas at 1200°, and 0.33 per cent at 1500°, remained; consequently these numbers probably represent equilibrium values, in presence of platinum, at the temperatures mentioned. 61. "Affinity Relations of Cupric Oxide and of Cupric Hydroxide." By ARTHUR JOHN ALLMAND. Crystalline cupric hydroxide is stable in ordinary moist air. When, however, it is shaken with alkaline or ammoniacal solutions at 25°, it loses water and becomes converted into cupric oxide. These two facts are apparently contradictory, and to explain them, tensimetric and electrometric experiments have been carried out, leading to the following results. (a) Freshly-prepared cupric oxide ages with time, and its free energy content thereby falls. (b) This ageing is attributed to increasing molecular complexity-not to crystallisation or to surface changesand is irreversible. (c) The explanation given accounts qualitatively for the electromotive behaviour of samples of copper oxide which have been subjected to varying thermal treatment, and may perhaps throw some light on phenomena noticed in the determination of dissociation pressures of certain oxides at higher temperatures. (d) The tensimetric and electrometric evidence shows that crystalline cupric hydroxide is stable with respect to freshly prepared cupric oxide and unstable with respect to aged samples of cupric oxide. A saturated solution of cupric hydroxide is unsaturated with respect to "fresh cupric oxide, and supersaturated with respect to "aged cupric oxide, which fact explains the apparently anomalous stability relations of cupric hydroxide, on the one hand, and cupric oxide and water on the other. (e) The free energy changes associated with a number of reactions at the ordinary temperature have been measured or calculated. (f) The dissociation pressure of cupric oxide at 1030° has been deduced, and shows excellent agreement with the experimentally determined values. 62. "3-Aminoquinoline and the Colour of its Salts." By WILLIAM HOBSON MILLS and WALTER HENRY WATSON. Quinoline-3-carboxylic acid has been prepared by a new method, and converted into 3-aminoquinoline, which exists in two forms, melting at 84° and 94° respectively. The salts of the base with one equivalent of acid are intensely yellow and fluorescent. The gradual addition of acid to the solution of a fixed amount of base is accompanied by remarkable variations of colour intensity, which are explained as being chiefly due to the formation of a semihydrochloride. In addition to a number of salts of the base, the following compounds have been prepared :Quinoline-3-carboxylamide, 3-acetylaminoquinoline, 3quinolineazo-B-naphthol, 3-hydroxyquinoline, 2-chloroquinoline-3-carboxylamide, 2-chloro-3-aminoquinoline. 63. "The Absorption Spectra of p-Toluidine, m-Xylidine, and of their Condensation Products with Acetaldehyde.' By JOHN EDWARD PURVIS. From an examination of the absorption spectra of the substances mentioned in the title, the author finds that (1) the absorption curves of p-toluidine and m-xylidine are very similar; (2) the condensation products with acetaldehyde show a disappearance of the more refrangible band of the original bases; (3) the isomeric a- and 8-condensation products show very slight differences in the persistencies of the bands; and (4) the addition of hydrochloric acid to the condensation products has no effect on the form or the persistency of the band. (To be continued). PAPERS were read as follows: Solutions." By T. G. BEDFORD. "Sturm-Liouville Series of Normal Functions in the Theory of Integral Equations." By J. Mercer. 'Solubility of Xenon, Krypton, Argon, Neon, and Helium in Water." By A. VON ANTROPOFF. Measurements of the Absolute Indices of Refraction in Strained Glass." By L. N. G. FILON. If light be transmitted through a slab of glass under tension T in a direction perpendicular to the line of stress, it is broken up into two components, polarised in planes perpendicular and parallel to the line of stress. If μ the index of refraction of the glass in the unstrained state, then, in the strained state, the indices of refraction corre be sponding to the above two components are u+C1T, μ + C2T respectively. The coefficients C1, C2 are spoken of as the stress-optical coefficients for the two rays. The present paper gives an account of measurements of C, and C2 according to a method described by the author in Roy. Soc. Proc., A, lxxix., 440. The measurements have been carried out on two Iena glasses bearing catalogue Nos. 0.935 and VV.3199 respectively, the first being a borosilicate, the second an "ultraviolet " glass. So far as is known this is the first series of absolute measurements of C, and C2 extending fairly continuously throughout the spectrum. The only previous measurements are due to Pockel (Ann. der Phys., 1902), and give the values of C1 and C2 for the sodium, thallium, and lithium lines only, obtained by quite a different method. The coefficients C1, C2 are found to be negative, so that both rays are accelerated by tension, but the effect is much larger for C2, i.e., for the ray polarised in the direction of stress. With regard to the dispersion in 0.935, both C, and C2 show a slight general decrease as we move towards the violet, but in VV.3199, C1 shows a decrease, whereas C2 shows an increase. The author published a paper in the Proceedings of the Society in 1893, showing how voltage v and current c are attenuated along a telephone or submarine telegraph-line, a line with resistance r, capacity k, inductance 1, and leakance s per unit length; currents are of the form sin qt. When lq/r is considerable the mathematical expressions become simple. It was pointed out that the introduction of is of great benefit. The author now points out that k may be made negative by the use of inductance leaks to earth, and I may be made negative by the use of condensers in series with the line. To introduce as Mr. Pupin has done by inductance coils at equidistant places on the line, or to introduce the other properties mentioned by placing | tions had removed a considerable amount of anxiety. As other contrivances at equal distances, is a mathematical problem of great complexity. Contrivances placed close together have the same effect as the continuous distribution of properties, but there is considerable expense; the problem is to find how far apart the contrivances may be placed so that the effect produced shall still be beneficial. Mr. Pupin has given a rule for the spacing of his coils, but practical men dispute its accuracy; nobody has given a rule for other contrivances; the object of the author is to give an easy method of calculation which is practically correct, and which can be used when the contrivance is any network or other combination of resistances, inductances, and capacities-some being leaks to earth-and it may include transformers, motors, and generators. Suppose there are contrivances at the equidistant places A, B, &c., m miles apart in a cable which has the above mentioned properties r, k, l, and s. There is a contrivance whose terminals are A and Ao, another whose terminals are B and Bo; between A and B there is m miles of cable. Let the currents in the line at A, A., and B be c, co, and C. Let the voltages at these points be v, vo, and V. The assumption on which the whole method is based is that V/C=v/c=p. This is practically true everywhere in a long line except near the ends. Now, whatever be the nature of the contrivance we can calculate vo and co from v and c. It is also known that n = √(r+lqi)(s+kqi). Putting V/C or p equal to v/c we have a quadratic to calculate and therefore V and C, and the problem is solved. Taking c = sin qt and calling it I then v = p. Whatever the contrivance may be we find that V = a + Bp and C = a+bp, where a, B, a and b are given in value; they are usually unreal quantities of the form M+Ni where i is I. Solving for p and finding C we have two answers which are reciprocals of one another. If (a+3) be called P, and this is very easily evaluated, then C = P√P2 – 1. Examples of the use of the method are given, some showing that the detached contrivances produce much the same and others very different effects from what might have been expected from a study of the cable with continuous properties. It was shown that a line may have contrivances somewhat far apart which will tune it to a musical note merely, so that it acts almost like an ohmic resistance, but which will not transmit well the currents of other frequencies, and that for the commercial transmission of speech there must be a compromise. The author impressed on the audience the fact that his method of calculation could be taught to quite non-mathematical people. a matter of fact, at the Post Office they had for some time past actually employed the formula, and had obtained a considerable amount of success in doing so, so far as the introduction of loading coils was concerned. For instance, a short while back, the question of a new cable between England and France was under consideration. It had been stated in foreign technical journals that the formulæ for "loaded" cables did not apply to the case of conductors covered with gutta-percha, owing to the very large electrostatic capacity introduced and the peculiarities of the insulation. Although he (Major O'Meara) had faith in these formulæ, still he felt that a practical experiment would remove all doubt, and in consequence he arranged an experiment with some old No. 7 gutta-percha wire, i.e., copper wire weighing 40 lbs. per mile covered with 50 lbs. of gutta-percha per mile, which had a resistance per loop mile of 44 ohms, and an electrostatic capacity wire to wire of 0.13 microfarad per mile. The gutta-percha wire was immersed in a tank, and experiments were conducted on lengths varying from 15 to 105 miles. They did not design special coils, but made use of some already in stock. These coils had an inductance of 83 millihenries, and a resistance of 13.4 ohms at 750 p.p.s. Admittedly the coils were not the best for loading this particular type of cable. Having decided to place these coils at 1 mile intervals, that is, to insert 55 m.h. per mile, they calculated the attenuation constant which would result. It worked out at 0.0427 per mile. When the coils were inserted, and the experiment completed, the observed attenuation constant was found to be 0.0419 per mile. From this it was evident that the calculated and observed results practically agreed. The information thus obtained enabled them to deal with the question of the new submarine telephone cable, and they decided that the attenuation constant for this cable should be o‘0147 per mile, to be obtained by the insertion of coils at one nautical mile apart. The coils have a resistance of slightly less than 6 ohms, and possess an inductance of o 100 henry at 750 periods per second. The cable has been manufactured and tested; the actual observed attenuation constant is o'0140 per mile, so that this again proved the value of the formula. The new telephone cable consists of 160 lbs. copper wire and 300 lbs. gutta-percha. It has a conductor resistance per loop mile of 12.5 ohms (excluding the coils) and a wire to wire capacity of 0.12 microfarad per mile. In an unloaded state, the attenuation constant of this cable is 0.045 per mile. Major O'Meara mentioned that the question of leakance was certainly of very great importance. It was owing to the very large part that leakance played that their first experiments were not successful. In America they had commenced to load aerial wires, and so large a part does this leakance play that in that country telephone engineers had been obliged to abandon the use of glass insulators, and substitute the highest grade of porcelain insulators to meet the difficulties which had been met with owing to an insufficient allowance for the part this factor played. feared that in no case could leakance be neglected, whether aerial or underground conductors were used. He Mr. A. W. MARTIN said that most telephone engineers in this country and America considered that a circuit should be capable of transmitting currents of frequencies varying from 100 to 2000 p.p.s. in order that good clear speech might result. For attenuation calculations, some take 750, and others 800 p.p.s. as a mean value. Where lq and kq are great compared with r and s respectively,— Major O'MEARA thanked Prof. Perry for his very in teresting and useful paper, and wished to assure him on behalf of a very large body of telephone engineers that they much appreciated the assistance which he and other mathematicians had rendered by their mathematical statement of the engineer's case. The equations given were of the same value to engineers as the compass was to the mariner. The only question they were in doubt about was whether all the forces that come into play had been equated. They consequently made a preliminary investigation of the manner in which the equations had been built up, and this convinced them that certainly the most important of the forces had been introduced into the equation. and writing s=0,— Some of them were responsible for the expenditure of large sums of public money, and the fact that they had something reliable to guide them in making their recommenda h The question is not whether so, but whether the ratio of s to k may be regarded as zero; since both are small quantities. In practice is found to be far from k negligible when inductance is placed in the circuit. When inductance L with resistance R is placed in leak, and assuming R small relatively to Lq, the impedance takes the place of ordinary insulation resistance, and is practically equal to Lq. The transmission efficiency of the whole circuit for low telephonic frequencies would be low, and there would be an appreciable CR loss in the leak coils. When I is not great compared with r, but where the insulation resistance is much above a megohm per mile, s may be neglected without causing calculated and observed results to differ materially. The expression then becomes mately equal importance ranging from the 2nd to the 11th harmonic. This would in itself explain why it was not only useless but absolutely harmful to tune to any particular frequency. Turning to the 18 ohm cable line referred to by Prof. Perry, he gave some results worked out by Mr. G. M. Shepherd. When this cable is in the normal condition the attenuation for a wave with a value q (angular velocity) of 1000 is 2.2 per cent, for a value of 5000 it is 31 per cent, and for 9000 6'4 per cent. This covered the whole commercial speech range, so that the variation over this range for attenuation is about 300 per cent. Using Prof. Perry's formula and taking his contrivances adding o 593 henry per mile, and a capacity of o'44 mfd. in series, it will be found that the variation of attenuation between q = 1000 and 9 = 5000 is 500 per cent. That is to say, up to the average frequency alone the variation in attenuation is 200 per cent more than over the whole range of speech frequency with the normal cable. But going a step further for an angular velocity of If be high compared with q no great error is made by 5550, the attenuation constant is o and the current at the writing but as in cable loops is never less than o'oor, it cannot be neglected except, say, when exceeds 50 ohms. The difference between the values of g and h becomes great as > becomes small. A circuit tuned to a particular frequency would be useless for telephone working, but might prove of value telegraphically. The ordinary paper and wax insulated thin lead-foil plate condenser offers resistance to the transmission of high frequency currents, and the insertion of such condensers in a telephone loop would be accompanied by a CR loss. Experimental results show that improvements of 370 per cent by coil loading (Pupin method) may be obtained in telephone loops. The 18 ohm per mile cable mentioned in the paper had a measured attenuation constant of o'045 per mile before loading. After the insertion of certain coals at 3.2 mile intervals, each coil having an inductance of o.133 henry and offering an effective resistance of 5'4 ohms at 750 p.p.s., the observed attenuation constant per mile was oo12, which result is fairly in agreement with the value of o o13 obtained by calculation at 750 p.p.s. from When the coils were placed at 2.1 mile intervals, calculation and observation gave the attenuation constant as 0.012 per mile. Coils with cores of properly chosen magnetic material give a higher inductance for a given effective resistance than air-core coils, and are therefore the better type. Experience shows that the quality of speech transmitted becomes bad when the number of coils per wave-length at 2000 p.p.s. is less than π. Measurements taken on various lengths of cable, the copper conductors in which were continuously and closely wound over with fine iron wire, showed that this "continuous" form of loading produces an improvement of only 60 per cent upon the untreated condition in cases where the copper is of 2 sq. mm. area and upwards. With smaller conductors it may possibly reach 100 per cent. Mr. B. S. COHEN said that the impressions obtained after reading this paper were that Prof. Perry had assumed that a telephone circuit tuned to the average telephonic frequency would as a result of this tuning transmit speechwaves more efficiently. He thought, however, that those who had studied this subject would agree that this was a misconception. He (Mr. Cohen) had previously pointed out that an average speech-wave consisted of a fundamental varying between 100 vibrations and 300 vibrations, the highest harmonic being about 1500 vibrations and the average vibration of the whole wave 800 vibrations. He had also given the Fourier series obtained by analysing a number of speech-waves, and this series showed that there are a large number of odd and even harmonics of approxi end of the line using the formula given is o. This means that the inductance and capacity bridge act as a shunt of infinitely low resistance. Any further increase in the frequency results in a negative attenuation, implying that an entire change in the nature of the transmission takes place. It would be of much interest if Prof. Perry would explain exactly what is the physical interpretation of this curious effect. Whatever the explanation, however, there is little doubt that the effect of this combination of bridges L and K would be satisfactory, as far as the commercial transmission is concerned, in spite of the fact that at 800 vibrations the attenuation is only 33 per cent, or an improvement for that particular frequency alone of about fifteen times which would be obtained by the application of the ordinary over the normal line. Contrasting these results with those Pupin series loading coils of o.13 henry each spaced at 1-mile intervals in the same line, the attenuation at any frequency over the range of telephonic speech is II per cent; that is to say, the volume improvement is 5, and the line acts as a distortionless one instead of amplifying the natural distortion of the unloaded line. He mentioned that this was not only a calculated result, but one that was amply confirmed by everyday practice, and which included the effect of the effective resistance of the inductance. Since his paper at the St. Louis Congress Prof. Kennelly had written a considerable number of papers on the subject of telephonic transmission, and his formulæ and methods were now adopted by many telephone engineers and were rapidly becoming standardised. Dr. RUSSELL thanked Prof. Perry for his instructive paper. He much appreciated the methods shown of getting simple approximate formulæ for some very difficult problems. It was interesting to compare the author's solution in the case when the leakage was zero with Heaviside's solution for a distortionless circuit. The only difference in the formula was that the attenuation was twice as great in the latter case. The Physical Society was deeply indebted to Major O'Meara and the other speakers for the very interesting data they had given about Pupinised telephonelines. From the theoretical point of view it was exceedingly satisfactory to find that the "loading coils' fulfilled their functions so efficiently and that their performance could be predicted so accurately. Dr. J. A. FLEMING forwarded the following communication:-The subject of Prof. Perry's paper has an interest for me at the present moment, as I happen to be giving a course of Post-graduate lectures at University College on the propagation of currents in telephone and telegraph cables. The method of representing the quantities concerned by complex quantities and their hyperbolic functions is of course very familiar to all who have paid any attention to the subject, and this method, aided by Mr. Blakesley's Tables of Hyperbolic Functions, enables arithmetic calculations to be easily made. Whilst it is quite true that the wave-form of the currents transmitted in telephony is very far from being simple harmonic, yet experiment shows CHEMICAL NEWS, Telephone Circuits. 129 that when using sine-curve currents having a frequency of | x/8, we have all the effects of smoothly distributed inabout 800 or an angular velocity of 5000, the results enable us to predict the effects with actual speech fairly well. The quantity it is important to predetermine is the current at the receiving end of a line of known length I and known constants, resistance, inductance, and capacity (R, L, C) per mile, when a receiver of known impedance z' = R'+jpL' is placed at the end. The important quantities are: the attenuation constant ductance but obtained more easily and with less expense. Mr. G. M. SHEPHERD, in a letter to the Secretary, observed that the system of introducing inductive leaks referred to in Prof. Perry's paper was presumably identical with what is termed "Thompson's " Compensated line. It could be shown that such a line was equivalent (proper spacing of loads assumed) to an ideal uniform line whose 2 (q2 LoL + RoR) constants are L'L L' R 2 (LoR LR。) where L, C, R are the ordinary wire constants, and Lo, Ro the inductance and resistance of the inductive leaks, s being the spacing. It could also be shown that the rule governing the spacing was virtually the same as that If Pl (where P = a+j8) is called the propagative length, formulated by Pupin for series coils. Looking at the and if = 2'/20 tanh g. then it is quite easy to show that the ratio of the currents at the receiving and sending ends is given by = cosh γ sech (Pl+7). 12/11 where V1 is the sending voltage. These formulæ are compact and easily applied in numerical calculations. The problem with which Prof. Perry is dealing is, however, that of the loaded cable. He does not make any reference to the important paper of G. A. Campbell (see Phil. Mag., March, 1903) or to that of Hayes (see Electrician, December 16, 1904), in which this problem is discussed. Campbell has given the following formula for the average or effective propagation constant P'a'+j3' | for a line consisting of impedance coils of impedance z' spaced out at intervals d on a line of propagation constant P and line impedance zo: matter from this point of view, it is seen that the effect of loading on the Thompson system is to reduce line resistance and inductance, or the inverse to the Pupin line. The two systems, however, appear to be essentially different, in that the Thompson line is really tuned or compensated, while the Pupin line is not. Hence the former is more or less subject to frequency, but the latter practically independent of it. A few cases worked out from the above formula for 18 w, 0.055 mfd. cable, with a 0·972 henry leak per mile, and several frequencies not far apart, give the following figures: but it is not certain that this formula can be trusted to give the true attenuation constant a' of the loaded line when dis much greater than about 1/8th of the waveProf. PERRY communicated the following reply :-"I am length on the loaded line, and when it is less than 1/8 glad to think that my paper has led to Major O'Meara's then the attenuation constant can more easily be calcu- remarks. The results of the Post Office experiments have lated by considering the added inductance and resistance been freely put before us by Mr. Martin; they are of smoothly distributed. Prof. Perry does not discuss the enormous value to people like myself who desire to make question of the loss of amplitude due to reflection from calculations. Such experiments are quite impossible for the interpolated impedances when these are spaced out to the ordinary student, they cost a great deal of money and large fractions of a wave-length, nor the advantages of the service of many assistants. I am very glad to think tapering off the loading at the ends of the loaded cable to that these results will be published in full by the Society. reduce the effects of these reflexion losses at the ends. As I regret that Mr. Cohen did not speak at much greater an illustration of the general accuracy of the formula for length, for he has for a long time been experimenting on the current ratios I may give the following figures, obtained behalf of the National Telephone Company, and the results for me by the kindness of Mr. Gill, Engineer-in-Chief of of his experiments would be of great value to students. the National Telephone Company, in their Research "I am afraid, however, that my paper has been a little Laboratory, by measurements made by Mr. Cohen. A misunderstood by these and other critics. They seemed standard line R=88 ohms, C=0·054 mfd., L = 0·001 henry, to think that I was advocating the use of a contrivance all per loop mile, had a receiving instrument of impedance consisting of condensers in the line and an inductance 660 66° 54′ vector ohms placed at a distance of fifteen leak, whereas I mentioned this contrivance merely to illus miles. The ratio of the sending to the received current by trate my paper. What I have endeavoured to do is to the above formula was found by calculation to be 5:36, show how calculations may be made by non-mathematical and by measurement with Mr. Cohen's barretter to be 53, people to find the effect of using any contrivance whatsothus showing a very good agreement. The frequency in ever. The above abstract does not, I am sorry to say, this case is 1000 vibrations. By the use of artificial indicate my praise of the work done by Prof. Kennelly, loaded lines it is easy to show experimentally the enormous who by his many papers and his valuable tables of cosh decrease in attenuation caused by properly loading the and sinh functions has cleared up many difficulties. It is line. Whilst we owe to Heaviside the first insistance on enough here to say that except the few lines devoted to the value of the added inductance, it is to Pupin we are Mr. Campbell's paper, the whole of Dr. Fleming's commore particularly indebted for proving that when immunication will be found to have been published by Prof. pedance is spaced out at distances not greater than about | Kennelly many years ago." |