286 British Association for the Advancement of Science. 
more than was necessary to allow the stern to pass through. Now 
the vessels were built with full sterns and narrow stems, with their 
maximum breadth at midships. For working well, however, a very 
deep keel was, he knew, necessary to give the helm full effect. In 
answer to the question whether these experiments might be made 
with model vessels on a small scale, Mr. Russell said that experi- 
ments with models were generally very fallacious and complicated, 
and that his had been made with vessels from seventy five to one 
hundred feet long. When asked whether they were made with or 
against tide, he replied that the existence of a previous current modi- 
fied the velocity of the wave, which was to be measured by the ve- 
locity of the water, not by the land.—Mr. Wenfall observed that 
Mr. Russell’s statements were corroborated by an observation of his 
‘own, that in an instance where the tide #ose thirty six feet, the effect 
of the lateral waves had been to form a rectangular excavation to 
four or five feet. 
~ On the Corroding of Iron by Salt Water.—Mr. Hartley read a 
paper, ‘on the corroding of iron by salt water.’ The object of the 
paper was to show that brass protects both bar and cast iron in a 
very perfect manner. The brass did not appear to have undergone 
any action, which, as stated by the President, is rather opposed to 
received notions of electro-chemical action. 
On some singular Modifications of the Ceknary Action of 
Nitric Acid on certain Metals.—Dr. Andrews next read a paper, 
‘on some singular modifications of the ordinary action of nitric acid 
on certain metals.’ Bismuth in nitric acid of specific gravity 1.4, 
was rapidly acted upon, but this action immediately ceased when 
the bar was touched by platinum. On removing the platinum from 
the liquor, the bismuth will sometimes begin again to dissolve; at 
other times, its surface will become covered with a black crust, 
which is soon removed by the acid; but the metal, though now ex- 
hibiting a beautifully polished surface, is no longer acted upon by 
the acid, or, at least, is dissolved only with extreme slowness. Thus, 
aslip of metal, which, in its ordinary state will require only a few 
seconds to complete its solution, will, when thus slightly modified, 
resist, for many hours, the action of the same acid. 
Copper and tin present similar phenomena, but zinc, when treated 
in the same way, has its oxidation and solution not arrested, but 
merely retarded. Arsenie was found to present a singular anomaly 
when heated in nitric acid, so as to give rise to effervescence : 
