214 



NA TURE 



[July 2, 1896 



The details ol the observations are given in precisely the same 

 manner as in the first paper, and formuhv of the Slotte type 

 showing the relation between viscosity in absolute measure and 

 temperature are calculated for each liquid. The general results 

 of the observations are then discussed in the same manner as in 

 the previous memoir. 



The conclusions relating to the graphical representation of 

 the results may be thus summarised. Both ethers and esters 

 give no evidence of molecular aggregation, and conform to the 

 rules that : — 



(1) In homologous series, the viscosity is greater the greater 

 the molecular weight. 



(2) An iso-compound has a smaller viscosity than a normal 

 isomer. 



(3) The more symmetrical the molecule of an isomeric com- 

 pound the lower is the viscosity. 



As regards the esters themselves, it is noteworthy, where the 

 comparison is possible, that : — 



(4) Of isomeric esters, the formate has the larger viscosity. 



As regards the algebraical representation of the results, it is 

 shown that in the expression ?) = C/(l + ;3'+ 7/-), derived 

 from Slotte's formula : — 



(i) In any homologous series, ;3 and 7 increase as the mole- 

 cular weight increases. 



(2) Of isomeric compounds, the iso-compound has the smallest 

 coefficient. 



(3) Ethyl ether, the symmetrical isomer, has smaller co- 

 efficients than methyl propyl ether. 



^4) As regards normal isomeric esters, the formate has the 

 largest, and the propionate the smallest coefficients, and the 

 values of the acetate are larger than of the butyrate. 



The authors then deal with the relationships existing between 

 the various viscosity magnitudes— the viscosity coefficient, the 

 molecular viscosity, and the molecular viscosity work — (i) at 

 the boiling point, and (2) at temperatures of equal -slope, the 

 slope adopted being that employed in their previous paper, 

 namely, o"04323, and values for the o.xygen in three different 

 conditions are given for each system of comparison in the same 

 manner as in their first communication. 



Physical Society, June 26. — Captain Abney, President, 

 in the chair. — Mr. F. Bedell read a paper on admittance 

 and impedence. The author discusses the application of the 

 method of "vector diagrams" to the solution of questions 

 connected with alternating currents. He shows how, by 

 a consideration of the loci of the different lines on such a 

 diagram, many problems which require for an analytical solution 

 a lengthy investigation, may be simply and expeditiously solved. 

 Mr. Blakesley asked the author what was his test of resonance ? 

 Was it that the primary current and E. M.F. were exactly in the 

 same or in opposite ]ihase ? Tlie term resonance was an acoustical 

 one, and he did not sec why it should be applied to one particular 

 case in the electrical problem. Mr. Inwards asked what degree 

 of accuracy the author had obtained. The author in reply said 

 that if the applied E.M.F. and the current were brought into 

 phase by means of a condenser in the secondary, then he called 

 that a case of resonance. The agreement between the experi- 

 mental and theoretical results was generally within from I to 

 3 per cent. — Prof S. P. Thompson read a paper on the 

 properties of a body having a negative resistance. The author, 

 after showing the consequences which would follow according to 

 the laws of Joule and Ohm if we postulate the existence of a 

 body having a negative resistance, goes on to .show how the 

 observations described by Messrs. Frith and Rodgers, in a paper 

 read at a recent meeting of the Society, only prove that that 

 part of the resistance of an arc, which is not constant, is a 

 positive resistance that varies inversely as the current. Since it 

 varies inversely as the current the term rfR/rfC will be negative, 

 and so will the quantity C{dC)/dR, which is what they have 

 tabulated as a negative resistance. That the resistance of the 

 arc itself should vary inversely as the current is natural, for it 

 may be regarded as a column of vapour, the cross-section of 

 which is proportional to the current, and therefore increasing in 

 its conductance in direct proportion to the current. There is no 

 need even to suppo.se any (distributive) adjuvant E.M.F., which 

 would be the other alternative to the suggestion they have made 

 Mr. Swinburne asked if the numbers on which Messrs. Frith 

 and Rodgers based their arguments were obtained by taking 

 successive readings of a voltmeter. Prof. .Ayrton said that what 

 they maintained was, that if the arc acts as if it had a back 



NO. 1392, VOL. 54] 



E.M.F. and a resistance, then the resistance is a negaiive 

 quantity. In ordinary cases we do not know what really consti- 

 tutes a resistance, but simply say that a circuit, in which electrical 

 energy is being dissipated at a rate proportional to the square of 

 the current, has resistance. If the loss is proportional to the 

 first power of the current, then we say there exists a back E. .M.F. 

 Is it impossible to imagine a circuit in which a loss of electrical 

 energy occurs proportional to the current, and a return of energy 

 to the circuit proportional to C- ? If in a curve showing the 

 relation between V and C you draw a tangent at any point, it is 

 not the tangent of the inclination of this tangent which Messrs. 

 Frith and Rodgers have called the resistance ; it is another 

 quantity, which they call the electrical il\' jdC. In conclusion 

 the author seems to have based his paper on three misconcep- 

 tions : (i) That it had been claimed that a negative resistance 

 could exist alone. (2) That the curves given by Messrs. Frith 

 and Rodgers showed that the ordinates were inversely pro- 

 portional to the current. (3) That what was measured was the 

 geometrical dV/dC. Mr. Frith said that in a paper by Mr. 

 Rodgers and himself, they had defined the resistance of the arc 

 as the ratio dV/dA, where by dV/dA they meant, not what was 

 ordinarily understood by this expression, but the value of the 

 ratio obtained by superpcsing an alternating current for a direct 

 current arc. In order to show that, in cases analogous with that 

 of the arc, but in which the true resistance can be verified, the 

 electrical dV/dC obtained by superimposing an alternating current 

 gives correct results for the resistance, .some experiments have 

 been carried out. In one case a glow-lamp was placed in series 

 with some fifty ampere secondary cells, and a current .sent through 

 against the E.M.F". of the cells. The value obtained for the 

 electrical d\'/dC agrees very well with the value of the resistance 

 obtained by dividing the P. D. between the terminals of the lamp 

 by the current. ' At very low frequencies for the .superimposed 

 alternating current it is evident that the electrical oscillations 

 would travel along the steady value curve, and this is clearly the 

 meaning of the critical frequency observed with cored carbons, 

 namely, that under the critical frequency the .superimposed 

 alternating current travels on the steady value curve, and over 

 that frequency along the line joining the point on the curve and 

 the instantaneous origin. — Mr. Frith exhibited a mechanical 

 model of the arc which he has devised. This model 

 consists of two rods of carbon dipping in two mercury 

 cups which are traversed by the current. The current also 

 passes through a solenoid which attracts an iron core attached to 

 the carbon rods and draws them down into the mercury, thus 

 reducing the resistance of the instrument. Hence it can be 

 arranged so that the P. D. between the terminals decrea.ses as 

 the current increases. With this model it is found that, for 

 superimposed oscillatory currents of such a frequency that the 

 moving parts are not able to follow the changes in the current, 

 the oscillations of the current and of P.D. are in phase, and the 

 electrical dV/dC gives the resistance of the apparatus for various 

 currents. Mr. Carter asked the author how on his vapour 

 column theory he explained the difterence in the behaviour of 

 solid and cored carbons. Mr. Enright asked why it was absurd 

 to suppose that a negative resistance could exist. Prof Ayrton 

 and Mr. Frith had made in their definitions certain restrictions : 

 it ought, however, not to be necessary to make any such 

 restrictions. Mr. Blakesley asked if, since the title of the ]>aper 

 by Messrs. Frith and Rodgers was entitled the " Iriic resist- 

 ance of the arc," it was to be inferred, as the results given were 

 negative, that a negative ohmic resistance existed in the arc. 

 Prof Thompson's paper appeared to him (Mr. Blakesley) to be 

 ratlier a mathematical than a physical paper. Prof Riicker 

 said that the discussion showed that considerable confiision 

 existed, and that the introduction of the term negative resistance 

 only tended to fog matters. It was entirely wrong to argue that 

 because you have a quantity with a positive value, therefore a 

 negative value must also be possible. .\s an example, take the 

 case of mass. If you defined as a positive mass that which is 

 attracted to the earth, and then found that cork when inmiersed 

 in water was repelled from the earth, would you therefore say 

 that cork had a negative mass? Is not " negative resistance " 

 a term for which some equivalent could be found which woukl 

 not lead to confusion ? Mr. Ilovendon made some remarks on 

 his experiments. The author in his reply said that he did not 

 dispute the accuracy of the results obtained by Messrs. Frith 

 and Rodgers, but it was the interpretation which they had given 

 of their results to which he objected. Mr. B'rith now makes a 

 new reservation, namely, that the results depend on the particular 



