286 Mr. J. Croll on the Wind Theory 



in presence of water effects the decomposition of that fluid — zinc- 

 hydrate and hydrogen being produced. 



According to Bonsdorff, arsenic does not dissolve in water 

 free from dissolved oxygen — a fact which we have verified, and 

 also that dilute sulphuric acid does dissolve it. 



If the foregoing view of the formation of AsH 3 be correct, the 

 hydrogen obtained by the action of the 1 couple upon water should 

 be free from arsenical gas, even though the couple be made with 

 arsenical zinc. 



We give the results of four experiments. A quantity of arse- 

 nical zinc-foil was "coupled" with copper, washed, and heated 

 with water ; and two litres of gas evolved were passed through a 

 tube heated to redness. Not a trace of arsenic was noticeable. 



A portion of the same foil not " coupled " was treated with 

 dilute sulphuric acid, and two litres of hydrogen evolved by the 

 action were passed through, a tube heated as before. 00019 

 grm. of arsenic was deposited in the cool part of the tube. 



The arsenical zinc with a covering of spongy copper, when 

 treated with dilute sulphuric acid, gave arseniuretted hydrogen, 

 which appears to point to the conclusion that it is not the cop- 

 per, but the inability of the arsenic to get into solution, that 

 accounts for the absence of hydrogen in the gas from water and 

 the couple — a conclusion that was confirmed by adding a dilute 

 solution of arsenic (1 part As 2 3 in 12,000 of water) to some 

 couple, when immediately the arsenical mirror was produced in 

 the heated tube. 



XXXIV. The Wind Theory of Oceanic Circulation. — Objections 

 examined. By James Croll, of H. M. Geological Survey 

 of Scotland *. 



IN my paper in the Philosophical Magazine for September, it 

 was shown by the temperature-soundings of the 'Challenger 3 

 Expedition that the surface of the North Atlantic must be 

 above the level of the equator, and that consequently, in so far 

 as that ocean is concerned, it is mechanically impossible that 

 there can be any such surface-flow as is assumed in the gravita- 

 tion theory. As this striking result has been questioned by 

 some physicists, I herewith subjoin Muncke's Table of the 

 expansion of sea-water, from which any one can readily satisfy 

 himself as to the accuracy of my figures. 



* Communicated by the Author. 



