TRANSACTIONS OF SECTION A. 497 



4. On the Determination of 'v' by means of Electric Oscillations. 

 By 0.3. Lodge, F.B.S., and R. T. Gl'azebkook, F.R.S. 



The autht^rs have recently'made a determination off, iisin<^ the oscillatory dis- 

 cliai-go of a condenser. The period of the discharpre, which passed between two 

 terminals connected through a circuit of measured self-induction to an air-condenser 

 of known capacity, was determined by forming an image of the spark on the edge 

 of a rapidly revolving photographic plate, the rate of revolution being accurately 

 asceitained, and examining the record micrometrically. 



5. On the Instruments tised in the recent Magnetic Survey of France. 

 By Professor A. W. RCckeb, M.A., F.B.S. 



A magnetic survey of France has recently been completed by M. T. Moureaux, 

 who has determined the magnetic elements at some seventy stations. A set of 

 instruments similar to those employed by him has recently been made under the 

 supervision of JI. iSIoureaux for the Science Museum at South Kensington, and 

 these were exhibited. 



The point aimed at in their construction was to secure accuracy combined with 

 dimensions and weight less than that of the Kew pattern instruments. The 

 weights of the magnetometer and dip circle are only 4 kg. and 2 kg. respectively, 

 and the results published by M. Moureaux show ahigh degree of accuracy. The 

 main points in the construction of the instruments are: (1) That the needles 

 used are much smaller than those used in the Kew pattern instruments. (2) The 

 end of the declination needle forms a concave mirror, and a reading is taken when 

 the image of a linear mark formed by this mirror is in the prolongation of another 

 line which is exactly opposite to the first on a thin piece of metal. (3) The geo- 

 graphical meridian is determined by a theodolite, which forms part of the appara- 

 tus, instead of by using — as in the Kew apparatus — a plane mirror to re ect the 

 image of the sun into a horizontal telescope. (4) Extremely fine siik thr ads are 

 able to support the small magnets used. (5) In the dip circle the o-raduated arc 

 rotates in its own plane about a horizontal ken when the 



end of the needle and its image formed by a small concave mirror attached to the 

 graduated circle coincide when viewed through a microscope. 



Bei^ort of the Committee on the Molecular Phenomena connected tvith the 

 Magnetisation of Iron. — See Reports, p. 33. 



7. On Magnetic Viscosity in Iron. By Professor J. A. EwiXG, F.B.S. 



The autlior described experiments showing that in certain circumstances the 

 process is gradual by which iron assumes magnetisation after the imposition of 

 magnetising force. The experiments are set forth in detail in the ' Proceedings of 

 the Uoyal Society ' for June 20, 1889. 



I 



SATURDAY, SEPTEMBER 14. 



The following Reports and Papers were read : — 



1. First Beport of the Committee for considenng the j)ossihility of calculating 

 Tables of certain Mathematical Functions, and, if necessary, of taking 

 steps to carry out the calculations and to publish the results in an 

 accessible form. — See Reports, p. 28. 



1889. 



K K 



