746 REPORT—1890. 
bility of basaltic rocks, to which he was led in the interpretation of the results of 
the great magnetic surveys made by himself in conjunction with Dr. Thorpe, by 
which remarkable disturbances due to magnetisation of the rocks and mountains 
were found ; (2) Quincke’s determinations of the magnetic susceptibility of liquids, 
The method proposed by the author consisted in measuring the mechanical force 
experienced by a properly shaped portion of the substance investigated, placed 
with different parts of it in portions of magnetic field between which there was a 
large difference of the magnetic force. A cylindrical or rectangular or prismatic 
shape, terminated by planes perpendicular to its length, was the form chosen; the 
component magnetic force in the direction of its length was equal to 3n(R?—R”)A ; 
where p» denoted the magnetic susceptibility, R, R’ the magnetic force in the 
portions of the field occupied by its two ends, and A the area of its cross-section, 
For bodies of very feeble susceptibility the best arrangement of field was that 
originally adopted by Faraday, and pushed so far recently by Professor Ewing, in 
the way of giving exceedingly intense fields. One end of the prism, or plate, or 
wire was in the air between flat ends and conical magnetic portions; the other 
might be in a place practically out of the field, or, if the portion of the substance 
given were exceedingly small, it might be in the field, but in a place of much less 
force than in the centre of the field. ‘The measurement of the magnetic force of 
the field was easily made by known methods: best by measuring the force ex- 
perienced by a short element of wire carrying a measured current. This portion 
of wire should be placed in the positions occupied by the two ends of the plate or 
wire of the substance, first in one position and then in the other. But when the 
second position was in a place of sensibly known force, the single measurement 
with the element of the wire in the first position sufficed. 
2. On the Tension of Water Surfaces, Clean and Contaminated, investigated 
by the Method of Ripples. By Lord Ray.etcu, Sec.R.S. 
The ripples were rendered visible by a combination of Foucault’s optical 
arrangement with intermittent illumination. Two frequencies were used, about 
43 and 128 per second. The principal results may be thus summarised. The 
tension of a water surface, reckoned in C.G.S. measure, is, in the various cases : 
Clean . : . 740 
Greasy to the point where the camphor motions nearly cease . 53:0 
Saturated with olive oil ; : : é ; 4 . 41:0 
Saturated with oleate of soda , : 3 A 25:0 
3. On the Adiabatic Curves for Ether, Gas and Liquid, at High 
Temperatures. By Professor W. Ramsay, F'.R.S. 
4, Report of the Committee on Electrolysis —See Reports, p. 138. 
5. Report on the State of our Knowledge of Electrolysis and Electro- 
Chemistry. By W.N. Saaw.—See Reports, p. 185. 
6. On the Action of Semi-permeable Membranes in Electrolysis. 
By Professor W. Ostwatvp. 
The author gave an account of experiments upon the passage of an electric 
current through solutions in series separated by semi-permeable membranes, and 
pointed out the importance of such phenomena to physiology. He explained that 
a semi-permeable membrane would allow ions of one kind to pass through, but 
