570 



REPOKT — 1894'. 



The molecular conductivity of solutions of acetic acid is abnormally low, and 

 in order to test whether the velocities of the ions were reduced in the same 

 proportion an experiment was made by a modification of Lodge's method, 

 which I had already used for tracing the course of other ions.^ A solution of 

 sodium acetate made first alkaline with soda and coloured red with pheuol-phthal- 

 lein was divided into two parts, and one of them decolourised 

 + _ with a little acetic acid. The solutions were thea placed in a 



r_ f idud of U tube with a vertical connecting limb (see figure), 



|— Jl ' rl— li so that the motion of the junction between the coloured and 

 imcoloured solutions could be easily followed. A current was 

 passed upwards across tlie boundary and the hydrogen ion tra- 

 velled with it, forming acetic acid and decolourising the phenol- 

 phthallein. It was found better in this case to use agar-jelly 

 solutions, which had been abandoned for other ions as intro- 

 ducing unnecessary complications. The velocity of the hydrogen 

 ion through a jelly solution of sodium acetate of strength 0'07 

 gramme equivalent per litre, when driven by a potential gradient 

 of one volt per centimetre, came out •00O0G5 cm. per second. 

 •Through a solution of hydrochloric acid of 0-1 gramme equi- 

 valent strength its velocity is -0030. The ratio of these numbers 

 is 1 : 46. The specific molecular conductivity of an acetic acid 

 solution of strength 0-07 is to that of a solution of hydrochloric 

 acid of strength 0-1 as 1 : 59. I have not yet been able to 

 devise a metliod for measuring the velocity of the acetic acid 

 group (CJII3O.,) in an acid solution, but the numbers given above 

 show that at all events the velocity of the hydrogen ion is reduced in about the 

 same proportion as the conductivity. 



MONDAY, AUGUST 13. 



The following Papers were read : — • 



1. On the Hesults of a New Analytical Representation of the Distribution of 

 Magnetic Force on the Surface of the Earth. By Ad. Schmidt, (f 

 Gotlia. 



The author has obtained in the first place three series in terms of spherical 

 harmonics for the three quantities aX sin v, /3Y sin v, yZ, where X, Y, Z are the 

 three components of the earth's magnetic force, v is the colatitude, and a, (i, y are 

 three factors, nearly equal to unity, depending on the spheroidal shape of the 

 earth. By a method which he has previously explained in the ' Archiv des 

 •leutschen Seewarte,' 1893, he deduces from these series three others which give 

 the magnetic potential on the surface of the earth : (1) as far as depends on forces 

 inside the earth, (2) on forces outside the earth. The third series represents that 

 part of the magnetic forces which cannot be expressed in terms of a potential, but 

 must be due to electric currents traversing the earth's surface. The first series has 

 been calculated to fifty-two, the second and third to forty-three coefficients. The 

 result shows an appreciable fraction of the magnetic force to be due to outside effects, 

 and also gives currents traversing the earth's surface, amounting on an average to 

 about O'l ampere per square kilometre. 



The author points out that thorouglily reliable results can only be obtained 

 after our knowledge of magnetic forces has been extended to higher latitudes in 

 the southern hemisphere. 



" Trans. U.S., 1893, A, p. 337. 



