Proceedings at the Meetings. 153 
3. The colour variations of the Fauna associated with Crinoids. 
(Preliminary note.) By F. A. Ports, M.A., Trinity Hall. 
4. The shortest line dividing an area in a given ratio. By 
N. Wiener. (Communicated by Mr G. H. Hardy.) 
5. Preliminary notes on some problems connected with Respiration 
in Insects generally and true aquatic forms in particular. By G. L. 
Purser. (Communicated by Mr F. A. Potts.) 
February 8th, 1915. 
In the Cavendish Laboratory. 
Dr Barnes, VICE-PRESIDENT, IN THE CHAIR. 
The following Communications were made : 
1. Theory of the Mobility of Negative Ions. By Professor 
Sir J. J. THomson. 
2. (1) The determination of the focal length of a thick mirror. 
(2) Experiment on the focal lines formed by refraction at a 
plane surface. 
(3) Calculation of the electrical resistance of a certain network 
of conductors. 
By Dr G. F. C. Sear.e. 
3. Determination of the thickness of thin plates by an inter- 
ference method. By C. T. R. Witson, M.A., Sidney Sussex College. 
4. The Wolf-note in bowed stringed Instruments. By G. W. 
Waite. (Communicated by Professor Sir J. J. Thomson.) 
February 22nd, 1915. 
In the Botany School. 
Proressorn NEWALL, PRESIDENT, IN THE CHAIR. 
The following Communications were made: 
1. On some Fossil Plants from the Devonian rocks of North 
Devon. By Dr Arser and R. H. Goons, B.A. 
