138 



M A M MALI A. 



stood to be about twenty minutes ; but it often plunges 

 to such depths as that more than this time would 

 elapse before it could get up again, if it had to pro- 

 ceed upon so long a slope as the action of the tail alone 

 would require. But, by the paws acting as a sort of 

 axle to it, it can turn the axis of the body upwards or 

 downwards with great rapidity ; and it can both de- 

 scend and ascend in nearly a perpendicular direction. 

 It sometimes descends with so much rapidity as seri- 

 ously to injure itself, by striking the bottom at a great 

 depth ; and Scoresby mentions an instance of a har- 

 pooned whale descending perpendicularly with so 

 much rapidity that it fractured its skull against the 

 bottom in a depth of 800 fathoms. At such a depth 

 the pressure on the body of the animal is far greater 



The Plunging Whale. 



than what it is nearer the surface ; but, as the differ- 

 ence of pressure between the two extremities is only 

 in proportion to the different depths of water above 

 them, the resistance of its descent is not proportionally 

 greater in deep water than it is nearer the surface. 

 Beyond a certain depth, however, it should seem that 

 the pressure of the water squeezes even the substantial 

 carcass of a whale together, so as to expel the air 

 from the lungs, and otherwise greatly increase its 

 specific gravity ; for when a wounded whale plunges 

 beyond a certain depth, it sinks in the abyss like a 

 stone, and never again returns to the surface. 



The cetaceous mammalia which frequent the fresh 

 waters, or are found only littoral or near the shores, 

 and which from this habit have no occasion to plunge 

 to such depths as the pelagic ones which range the 

 wide oceans, have not the same enlargement of the 

 bones of the face, and it is obvious that, from the 

 comparatively small depth of water in their haunts, 

 they have not the same occasion for it. 



The two kinds of organs of motion in the mam- 

 malia, of which we have given a slight notice, in the 

 structure and action of what may be considered as 

 the most perfect or typical form of each, may be con- 



sidered as one general class, namely, motion in a 

 animal taking its origin from a fluid as a fulcrum 

 and this general class readily divides itself, accorditi 

 to the nature of the fluid which serves as the lulcrmi 

 into two sub-classes or orders. The first of thes< 

 and that which we may presume to require th 

 greatest effort from animals having the general strut 

 ture of the mammalia, is motion originating in atmc 

 spheric air, which we have exemplified in the bi 

 family, the only mammalia which in reality are caps 

 ble of performing it. The second is that where wate 

 the other abundant and generally distributed flui 

 connected with the earth, affords the fulcrum. Thi 

 from its greater specific gravity, more nearly af 

 preaches to being the natural element of the man 

 malia than the other does ; and therefore, as we hav 

 said, there is scarcely any of the mammalia but whic 

 can originate motion from the resistance of water, s 

 as to keep its body buoyant in that fluid, at least fc 

 some time. If, however, the animal has not, in th 

 structure of its organs of motion, some adaptation t 

 the water, progressive motion through the water i 

 far more fatiguing to it than progressive motio 

 through the air with the earth as a fulcrum froi 

 which to start each successive movement. Thei 

 are two causes explanatory of this : in the first plac 

 the motion of the animal has far more resistance t 

 overcome in the water than it has in the air ; and i 

 the second place the fluidity of the water makes 

 give way to the stroke of the foot, in such a manm 

 as that great part of the effort is wasted in the recoi 

 and it is only the surplus after this waste which CH 

 go to the progressive motion in the animal. VV 

 have a very familiar but very forcible illustration ( 

 this, in the different rate of current which a man ca 

 stem with ease in the air from what he can stem i 

 the water. The wind or atmospheric current ma 

 be blowing at the rate of twenty, fifty, or even mor 

 miles in the hour, and yet a man who leans forwar 

 upon it, and gives himself the advantage of the ber 

 leg in front and the straightened leg in the rear, ca 

 not only keep his ground but make tolerably rapi 

 progress against it. If, however, a current of th 

 water sets even nearly as fast as a man can walk o 

 land against a pretty stiff breeze, the current of th 

 water bears him along with it in spite of his utmo! 

 efforts. There is no doubt that, on the land, the ma 

 has the advantage of the solid fulcrum to spring fron 

 and also of the comparatively small resistance of th 

 gaseous fluid against which to make his advance 

 while, in the water, he has to make his way agains 

 the resistance of the denser fluid, and at the sam 

 time the current bears his fulcrum away from hir 

 with a rapidity proportional to its velocity. 



It is not difficult to give a rude estimate of th 

 different resistances with which the man has to cor 

 tend in these cases. In round numbers, the weigli 

 or power of resistance in water is about 800 times a 

 much as that in atmospheric air ; and, as it is gent 

 rally understood that the impetus or effect of bodie 

 in motion is directly as their quantities of matter, an 

 inversely as the squares of their velocities, if a man' 

 body presented the same surface to the wind as t 

 the water, the mere resistance of the water alon 

 without any motion would be equivalent to that of 

 current of air having a velocity of about twenty-eigli 

 miles in the hour. But as a man does not swir 

 through the water as he walks through the air, it i 

 not easy to state the proportion of the resistances ii 

 any thing like correct terms. It is also to be take; 



