THE CLOUD llEGION, ETC. 273 



most simple plan for determining the velocity of Avaves — and it 

 may be hourly practised on board of every vessel — is the plan 

 which is followed by Captain Ginn, of the American ship John 

 Knox, one of our co-operators. AVhen he heaves the log with the 

 8eas 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 liorn 26-8.* 



508. Determining the lieiglit of clouds at seo.. — It would afford a 

 pleasant and agreeable diversion for a squadron of men-of-war, 

 as they pursue their voyage at sea, to amuse themselves and 

 instruct their friends at home with observations upon all such 

 phenomena. Those who are wdlling to undertake the clouds 

 will have no difficulty in devising a plan both for the upper and 

 the lower strata. 



509. Cloud region at sea in the sha^e of a double inclined plane. — 

 Over the land the cloud region is thought to vary from three 

 to five miles in height ; there the height of clouds is known to be 

 ver}' variable. At sea it is no doubt less so. Here the cloud 

 region is somewhat in the form of a double inclined plane, 

 stretching north and south from the equatorial cloud-ring as a 

 sort of ridge-pole. In the balloon ascents which have taken 



* From Captain Ginn's Abstract Log : — 



"Saturday, September llth, 1858, doubling Cape Horn. The long regular 

 swell during this part of the day aiForded me another opportunity of trying the 

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

 ei|ual to 13 knots with the 14r-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 

 1 ime, and then noting where the crest of a 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, namely, 22 to 23 miles an hour; but to-day I found it to be consider- 

 ably 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-cliip was 

 towing astern (13 knots) to just ahead of the ship. The length of the ship is 

 equal to about 6i knots : the ship's speed at the time was 8 knots ; thus, 

 13-f-6|-r8 = 27|. A few days ago I tried the same experiment, and found the 

 velocity to be 22 to 23. What has accelerated the velocity of these waves? 

 Have the soundings anything to do witli it ?"' 



T 



