SCIENTIFIC SUMMARY. 
183 
5. Near the last house in the village of Theddes a vein of leptynite, 80 
centimetres thick, is cut nearly at right angles by a vein of pegmatite with 
tourmaline of about equal size. 
The formation of all these rocks is considered by the author to have, 
taken place during the Silurian epoch. 
PHYSICS. 
A Note on the Determination of the Magnetic Inclination in the Azores 
is communicated to the Proceedings of the Royal Society by Dr. Thorpe. 
He notes that except a series of similar observations made by the officers of 
the Challenger in 1873, none have been made since Captain Vidal’s survey in 
1843. Magnetic observing is difficult in these islands, from the intensely vol- 
canic nature of the strata. The dip-circle used was lent from Owens College, 
Manchester. In the island of St. Michael the mean dip was 62° 4CP2 N., 
against 63° 56'*8 N. of the Challenger. In Terceira it was 64° 10 r, 3, and in 
Faya! 63° 38'*5. 
The Thermo-electric behaviour of Aqueous Solutions, with Platinum 
Electrodes, has been further studied by Dr. Gore, in continuation of his 
memoir, already abstracted in this Summary. To prevent suspicion of error 
from chemical action upon the mercury electrodes therein used, coiled 
ribbons of sheet platinum were substituted for mercury, all other parts of 
the apparatus remaining exactly similar to those employed in the former 
experiments. They were heated to redness and thoroughly washed. Pre- 
cisely similar liquids were used as in the first researches, none of them acting 
chemically on platinum. These were boiled for half-an-hour to expel dis- 
solved air. At 180° Fahr. cyanide of potassium made hot platinum IPO 
positive ; whereas the same couple, with sulphuric acid 1 in 40, rendered it 
4’25 negative. Between these extremes is a list of thirty-four other sub- 
stances. This is compared with the former series, and the differences between 
the results are only in one or two cases important. The chief conclusion 
arrived at is that the currents previously obtained with mercury are really 
due to heat, and not to minute amounts of chemical action. 
The same observer also contributes memoirs on the Influence of Voltaic 
Currents on the Diffusion of Liquids and on Electric Osmose. In the former 
case the phenomena are very complex, consisting of a mixture of physical 
and chemical effects, chiqfly due to electrolytic changes, to differences of 
specific gravity, to ordinary liquid diffusion, to electrolytic transfer, and to 
heat of conduction-resistance. In the latter instance the experiments were 
similar to that made by Porrett. A vessel of thick glass divided vertically 
into two equal parts, had a diaphragm of biscuit porcelain about P5 millim. 
thick between its two cavities. The cell was held together by screw clamps. 
The electrodes were of sheet platinum, the current from several Grove’s 
pint-cells in single series, al ways in the same direction. In sixty-eight experi- 
ments osmose occurred in all but one — a saturated solution of potassic cyanide. 
It was in the same direction as the electric current, with one exception, that, 
namely, of bromide of barium in absolute alcohol. This single fact quite 
