Mathematical and Physical Science, 301 



considered and repeated, subsequently yielded, in much ac - 

 cordance with the former, a total width, in the line of the 

 ship's course, of about 600 feet. 4. But the total distance 

 betwixt the crests of two waves, then reckoned at 550 feet, 

 a distance passed by the wave in 16*5 seconds of time, by 

 no means indicates, it is obvious, the real velocity of the 

 wave, as the ship meanwhile was advancing merely in the 

 same direction at the rate of nine knots, that is, nine geo- 

 graphical miles, or (6,0756 feet x 9 = ) 54,6804 feet per hour, 

 or 15-2 feet per second. During the time, therefore, of a 

 wave passing the ship = 16*5", the ship would have advanced 

 on its course 165 x 15-2 = 2506 feet. Reducing this for the 

 obliquity of two points, we have 231*5 feet to be added to 

 the former measure, 559 feet, which gives 790-5 feet for the 

 actual distance traversed by the wave in 16'5 seconds of time, 



, . ^ ^, ^ ,. /3,600"x790-5 ^-,^o-1^7r X 

 bemg at the rate of I ^70= = ) 17,2d1-7 feet, or 



3267 English statute miles per hour. To know how far 

 this result is but proximate, it should be considered that, of 

 the several elements employed in the calculation, all but one 

 might be deemed accurate. The interval of time occupied 

 by the transit of a wave with respect to the position of the 

 ship, the direction of the ship's motion with relation to 

 that of the waves, and the speed of the ship through the 

 water, — may all be recorded as essentially accurate. The 

 element in doubt is that of the average distance from sum- 

 mit to summit of the waves. This distance, it has been 

 seen, was, by a twofold process of observation or compa- 

 rison accordantly assumed. The value of the judgment 

 derived from rapid comparison of measures by an eye accus- 

 tomed to such estimations is, it should be observed, far 

 higher than might be generally considered. The practical 

 military commander or engineer officer is able to make, by 

 mere inspection of the ground before him, remarkably close 

 estimates of spaces and distances. When engaged in the 

 Arctic whale fishery, I was enabled, from habit and compa- 

 rison of unmeasured spaces with known magnitudes, to esti- 

 mate certain distances with all but perfect accuracy. Thus, 

 as to a circumstance in which we were most deeply inte- 



