272 THE niYSicAL geography of the sea. 



hoped that they will. Observations here are to be made rather 

 under the direction of the commander of a fleet or squadron than 

 of a single ship, and it is hoped that some of the distinguished 

 admirals and brave old commodores "who cruise about the world, 

 with willing hearts and ready hands for the cause we advocate, 

 may signalize their flag by contributing, for the advancement of 

 human knowledge touching the physics of the sea and the ma- 

 chinery of the air, a series of well-conducted observations upon 

 the force of the trade-winds,* upon the height and velocity of the 

 clouds, the height and velocity of the waves, etc., in different parts 

 of the ocean. 



507. Commodore Wiillerstorf, of the Austrian frigate ISTovara, 

 Height and velocity made au interesting series of observations upon the 



of waves — plan for , . t , i t •, r ^^ i • x.' 



determining. height and vclocity 01 the waves durmg his cruise 



in that vessel upon his last scientific mission. These no doubt 

 will be published with the other important results of that admira- 

 bly-conducted expedition. The most simple plan for determining 

 the velocity of waves, and it may be hourly practiced on board 

 pf every vessel, is the plan which is followed by Captain Ginn, of 

 the American ship John Knox, one of our co-operators. When 

 he heaves the log with the seas following, instead of hauling in 

 the line immediately, he leaves the chip to tow, watching till he 

 observes it on the crest of a wave ; he then turns the glass, or 

 notes his watch, and marks the time it takes the wave to reach 

 the ship. The usual velocity of the waves in the Atlantic is 22-3 

 miles an hour, off Cape Horn 26-8.t 



508. It would afford a pleasant and agreeable diversion for a 



* See Maury's Sailin.Gj Directions, vol. ii., "Average Force of the Trade-winds." 



f From Captain Ginn's Abstract Log. 



" Saturday, September 11th, 1858, doubling Cape Horn. The long regular swell 

 during this part of the day afforded me another opportunity of trying the velocity 

 of the waves. This I did by paying out the log-line enough to be equal to 13 knots 

 with the 14-second glass ; then by watching the chip — to which I had fixed a piece 

 of white rag to render it more distinguishable — as it appeared on the crest of a well- 

 defined wave, and turning the glass at the same time, and then noting where the 

 crest of the wave is at the moment the glass is ' out. ' 



" I have several times before tried the experiment in this way with the same length 

 of line out astern, and have always found about the same rate for the velocity, name- 

 ly, 22 to 23 miles an hour ; but to-day I found it to be considerably more, namely, 

 26 to 28 miles an hour. Thus the crest of a wave would pass, while the 14-second 

 glass ran out, from the place where the log-chip was towing astern (13 knots) to just 

 ahead of the ship. The length of the ship is equal to about Q\ knots ; the ship's 

 s:)ef'd at the time w.is 8 knots ; thus 13 + 6V4-8^27.V. A few dnys ago I tri^d the 



