TRAJ!^SACTIONS OF SECTION A. 643- 



electromotive force would have been if there had been no changes caused either 

 by dilution or by chemical union. . 



All the facts appear to be consistent with the theory that dilution increases 

 and chemical union decreases the freedom of molecular movement. 



7. A Lecture-room Volt- and Amperemeter. 

 By Professor F. G. Bailt. 



A d'Arsonval galvanometer of moderate resistance is used, and a powerful 

 lantern throws a conspicuous circle of light on to a large semi-transparent scale. 

 A high resistance and a set of shunts allow of the measurement of electromotive 

 forces, the scale being adjusted to read directly in volts or multiples, and a range 

 of '05 volt to 300 volts being obtained. By the omission of the high resistances 

 the galvanometer and shunts maybe used for ordinary purposes, and may be adjusted 

 to measure thermo-electric forces. Currents from '5 milliampere up to 30 amperes 

 are measured by the difference of potential between the ends of a low resistance, 

 two alternative resistances being used, and the range is improved by the use of 

 resistances in series with the galvanometer. A tapping and a reversing key are 

 fixed on the box. 



8. On the Phosphorescent Gloio in Gases. 

 By John B. B. Burke, M.A. 



When a ring or electrodeless discharge is sent through a gas an after-glow is 

 produced, at pressures within certain limits, in air varying between 0'7 mm. and 

 ()'02 mm. A series of experiments was carried out to investigate the cause of 

 this glow, and it was found that it was due to particles which do not carry a 

 charge of electricity, but nevertheless produce conductivity in the gas as they pass 

 through it. They are not stopped in their motion through charged wire-gauze 

 electrodes, nor by an electromotive force, and yet cause a current to pass between 

 two such electrodes situated lower down in a long vacuum tube. The glow 

 diffuses through narrow brass tubing which is well earthed, proving that the glow 

 itself does not carry a charge. When the diffusion takes place through a brass 

 tap between two large bulbs the glow lasts three or four times as long in the one 

 that the discharge has not passed through ; and it was found that the glow in the 

 former was destroyed instantaneously when a discharge was sent from a small 

 induction coil between two electrodes in a side tube, showing that the glow was 

 destroyed by the ionised gas. 



The conductivity observed was probably due to the breaking up of the phos- 

 phorescent molecules by the ions produced by the spark as the glow moved through 

 them. 



MONDAY, SEPTEMBER 10. 

 The Section was divided into two Departments. 

 The following Reports and Papers were read : — 



Department I. — Mathematics. 



1. Repoi-t on Tables of certain Mathematical Functions. 

 See Reports, p. 46. 



2. Report on the Present State of the Theory of Point-Growps. 

 See Reports, p. 121. 



T T 2 



