TRANSACTIONS OF SECTION A. 581 



By turning the micrometer screw of tlie pendulum-interruptor, and thus chang- 

 ing tlie distance between the contacts, t can be varied and a large number of points 

 on the logarithmic curve found. By a process of calibration with the pendulum, 

 it was found that the electrometer-throws were strictly proportional to the poten- 

 tials Pfy This calibration was made by taking a w so small that the exponential 

 term vanished and measuring p for various p^s. 



The resistances used were made by ruling pencil lines upon finely-ground glass, 

 upon the ends of which a thin film of platinum had been firmly deposited by bum- 

 ing in and soldering the connecting wires to this, giving a firm and reliable con- 

 nection to tlie resistance. 



The condenser was a large plate-condenser, 50 cm. in diameter, whose capacity 

 was found by Kirchhoft''s formula. Three capacities, 350'204, 770-513, and 

 998'459 cm. were used, with resistances of from one-half to five megohms. 



The time-constant of the pendulum was found by the method of Pouillet for 

 short intervals, by means of a ballistic galvanometer. One division of the micro- 

 meter was found to correspond to 



ia346 X 10-5 sec. 



In the experiments, readings were taken at intervals between 100 and 2,000 

 micrometer-divisions. 



A large number of observations was taken, in which all the measured quanti- 

 ties c, XV, and t were varied. 



The value of v arrived at was 



2-987 X lO'o cm. sec-» 



4. On the Magnetic Field in the neicjhhourhood of the South London Elec- 



trical Eaihvay. By Professor W. E, Ayeton, F.B.S., and Professor 

 EiJCKEK, F.B.S. 



Observations were made by means of a mirror galvanometer the period of 

 ■which was 10 sec, and which was used as a magnetometer. The instrument was 

 placed in two rooms about 70 and 180 feet respectively' from the centre of the 

 road, under which the railway runs at a depth of about 70 feet. It is belisved that 

 the earth was acting as the return portion of the circuit. In accord with this 

 the instrument was found to be in continual vibration. The amplitude of the 

 swing at the station nearer to the railway was often 50 mm., and the law of decrease 

 with distance appeared to be inversely as the first power. It is, therefore, evident 

 that experiments of the most ordinary accuracy could not be made within a very 

 great distance of such a railway. 



5. On the Periodic Time of Timing-ForJcs maintained in Vihration Elec- 



trically. By Professor J. Viriamu Jones and T. Harbison. 



6. Magnetic Experiments made in Connection with the Determination of the 

 Hate of Propagation of Magnetisation in Iron. By F. T. Tkouton. 



7. On the Connection "between the Crystal Form and tlie Chemical Compo- 

 sition of Bodies. The Symmetry of Crystals accounted for by the 

 Application of Boscovicli s Theory of Atoms to the Atoms of the Chemist. 

 By William Baklow, F.G.S. 



After mentioning that he read papers on the same subject at the meetings of 

 the British Association at Aberdeen in 1885 and Leeds in 1890, the author states 

 that he is now prepared to deal with the matter in a more general way, and to 

 submit proof that the mutual interaction of ditierent kinds of atoms present in 



