THEIR USE IN RESISTING PRESSURE. 345 
are simple curves, becoming foliated at their 
junction with the outer shell, and thus distri- 
buting their support more equally beneath all 
its parts, than if these simple curves had been 
continued to the extremity of the transverse 
plates. In more than two hundred known 
species of Ammonites, the transverse plates pre- 
sent some beautifully varied modifications of 
this foliated expansion at their edges ; the effect 
of which, in every case, is to increase the 
strength of the outer shell, by multiplying the 
subjacent points of resistance to external pres- 
sure. We know that the pressure of the sea, at 
no great depth, will force a cork into a bottle 
filled with air, or crush a hollow cylinder or 
sphere of thin copper ; and as the air chambers 
of Ammonites were subject to similar pressure, 
whilst at the bottom of the sea, they required 
some peculiar provision to preserve them from 
destruction,* more especially as most zoologists 
* Captain Sm^'th found, on two trials, that the cylindrical 
copper air tube, under the vane attached to Massey's patent log, 
collapsed, and was crushed quite flat under a pressure of about 
three hundred fathoms. A claret bottle, filled with air, and well 
corked, w^as burst before it had descended four hundred fathoms. 
He also found that a bottle filled with fresh water, and corked, had 
the cork forced at about a hundred and eighty fathoms below 
the surface ; in such cases, the fluid sent down is replaced by 
salt water, and the cork which had been forced in, is sometimes 
inverted. 
Captain Beaufort also informs me, that he has frequently sunk 
corked bottles in the sea more than a hundred fathoms deep. 
