FISHES. 229 



The reason why a wedge shaped piece of timber requires a 

 greater force to draw it through the water sharp end foremost 

 appears to be this : — the wood occupies in water a certain space, 

 by changing its situation a vacancy is formed, which is instantly 

 filled up by the surrounding water. Since the water itself is 

 inert, it is evident that its disposition to follow the wood, and fill 

 up the vacancy left by it, can be only produced by ,the joint 

 action of its own gravity and atmospheric pressure ; therefore, the 

 vfeiocity with which it can follow the wood will always be less 

 than that of the wood itself, and this disproportion will be greater 

 as the velocity of the wood increases; consequently, the resistance 

 offered to it in front will be increased by the partial vacuity 

 existing behind it from the sluggishness with which the water 

 follows to fill it up. When moving butt end foremost this does 

 not take place ; because the tapering form not only enables it to 

 leave the surface of the water, with which it was in contact more 

 gradually, but, by allowing it to act laterally, in filling up the 

 space left by it, no after current is produced. 



J. N. H. 



ON THE GEOGRAPHICAL DISTRIBUTION, HABI- 

 TAT AND MIGRATIONS OF FISHES. 



In the general view of the nature and organization 

 of Fishes which has lately appeared in Mr. Griffith's 

 version of Baron Cuvier's "Animal Kingdom," Lieut. 

 Col. Hamilton Smith, ahthor of this part of the 

 work, has introduced his observations on the geo- 

 graphical distribution, habitat, and migrations of 

 fishes, and communicated from his own researches 

 several facts which bear strongly upon the conditions 

 of existence which Providence appears to have im- 

 pressed upon this class of animals. BeUeving that 

 there is much of curious interest in the inquiry ; we 

 deem it will prove acceptable to our readers to have 

 some parts of his corrected and revised munuscript, 

 on this subject, laid before them ; we shall therefore 

 merely premise, that having first described, mostly 

 in the animated language of the baron, the general 



