TRANSACTIONS OF THE SECTIONS. 29 
2. The periods of regular waves, in incidental series, overtaking the ship, were ob- 
served as follows :— Waves. Min. Sec. Mean. 
20 occupied 5 30=16!'"5 
10 oe Oe 35=T5 Ὁ 
10 » 2 50=17°0 
10 ne 2 45=16°'5 
8 a3 2 16=17 Ὃ 
General average......--....16 °5 
3. The length of the ship was stated to be 220 feet. The time taken bya regular 
wave to pass from stern to stem, appeared, on a mean of several observations, to be 
about six seconds. 
Hence 6” : 220 ft. (the width passed over in that time) : : 16°5 to 605 feet (the 
width passed over betwixt crest and crest). But this extent, by reason of the obli- 
quity of the direction of the waves to the course of the ship, is found to be elongated 
about 45 feet, reducing the probable mean distance of the waves to 559 feet. 
Independently of this process, I had previously estimated the distance of the 
wave-crests ahead and astern, when the ship was in the hollow, as I stood near the 
centre of the ship’s length on the paddle-box, at 300 feet each way, by comparing 
the intervals betwixt my position and the place of the wave-crest with the known 
length of the ship. This comparison, frequently reconsidered and repeated subse- 
quently, yielded, in much accordance 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, thus reckoned at 559 
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 
nearly in the same direction at the rate of nine knots, that is nine geographical miles, 
or (6075°6 feet x 9=) 54680°4 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 16°5 X 15°2=250°6 feet. Reducing this for the obliquity of two points, 
we have 231°5 feet to be added to the forrner measure, 559 feet, which gives 790°5 
feet for the actual distance traversed by the wave in 16°5 seconds of time, being at 
the rate of se ak ae 17251°7 feet, or32°67 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 ail be received as, essentially, 
accurate. The element in doubt is that of the average distance, from summit to 
summit, of the waves. This distance, it has been seen, was, by a twofold process 
of observation or comparison, accordantly assumed. The value of the judgement de- 
rived from rapid comparison of measures by an eye accustomed to such estimations, 
is, it should be observed, far higher than might be generally considered. The prac- 
tical 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 comparison of 
immeasured spaces with known magnitudes, to estimate certain distances with all 
but perfect accuracy. Thus, as to a circumstance in which we were most deeply in- 
terested, the near approach of a boat to a whale, I found it quite practicable, 
whenever the pursuing boat approached within twice or thrice its length (except 
when the position was near end on); to estimate the distance to less than a yard. 
Now the means of comparison, by the eye, as to the estimation of the breadth of 
the Atlantic waves, was that of the ship’s length of 220 feet. When the ship was 
_ fairly in the middle of the depression betwixt two waves, it was assumed, with refer- 
ence to this known measure, that something obviously less, but not greatly so, than 
the ship’s length was the distance of each of the two waves then contemplated, 
giving a total width of about 600 feet. But the comparison of the time required by 
a wave to pass from stern to stem, with the average time of transit of an entire 
wave, yielded a much better result ; and, on much consideration of the subject, I am 
inclined to believe that the estimate is a literally close approximation to the truth. 
