THEIR USE IN RESISTING PRESSURE. 261 



At PI. 35, from d. to e. we see the edges of the same trans- 

 verse plates which, in PI. 36, 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 present 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 pressure. 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 Ammo- 

 nites 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 

 agree that they existed at great depths, " dans les grandes 

 profondeurs des mers."f 



Here again we find the inventions of art anticipated in 



* Captain Smyth found, on two trials, that the cyUndrical copper air tube, 

 vuidei" the vane attached to Massey's patent sounding machine, collapsed, 

 and was crushed quite flat under a pressure of about three hundred fathoms. 

 A claret bottle filled with air, and well corked, was burst before it had de- 

 scended 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 thaii a hundred fathoms deep, some of them empty, 

 and others containing a fluid. The empty bottles were sometimes crushed, 

 at other times, the cork was forced in, and the bottle returned full of sea 

 water. The cork of the bottles containing a fluid was uniformly forced 

 in, and the fluid exchanged for sea water; the cork was always returned to 

 the neck of the bottle, sometimes, but not always, in an inverted position. 



f See Lamarck, who cites Bruguieres with approbation on this point. — 

 Animaux sans: Vert: vol. vii. p. 635. 



