40 HABITS OF THE SPERM WHALE : 
laterally and obliquely, it strikes the water with the 
broad flat surface of the flukes in a direct manner, 
upwards and downwards, and each time the blow is 
made with the inferior surface, the head of the whale 
sinks down to the depth of eight or ten feet, but when 
the blow is reversed, it rises out of the water, presenting 
then to it only the sharp cutwater-like inferior portion. 
The blow with the upper surface of the flukes appears 
to be by far the most powerful, and as at the same time 
the resistance of the broad anterior surface of the head is 
removed, appears to be the principal means of progression. 
This mode of swimming, with the head alternately in 
and out of the water, is called by whalers 64 going head 
out/ 5 (see cut, p* 83, fig. 1). And in this way the 
whale can attain a speed of ten or twelve miles an hour, 
and this latter, I believe to be his greatest velocity. 
The tail is thus seen to be the great means of pro- 
gression, and the fins are not much used for that pur- 
pose ; but occasionally when suddenly disturbed, the 
whale has the power of sinking quickly and directly 
downwards in the horizontal position, which he effects 
by striking upwards with the fins and taih 
