J. Croll — Influence of the Gulf-stream, 159 



tlial ot a stream 50 miles broad and 1000 feet deep, flowing at 

 the rate of four miles an hour. And the mean temperature of the 

 entire mass of moving waters is not under 65'^ at the moment of 

 leaving the Gulf."^ I think we are warranted to conclude that the 

 Gulf-stream, before it returns from its northern journey, is on an 

 average cooled down to at least 40°, consequently it loses 26° of 

 heat. Each cubic foot of water, therefore, in this case carries from 

 the tropics for distribution upwards of 1500 units of heats, or 1,158,000 

 foot-pounds. According to the above estimate of the size and velocity 

 of the stream 5,576,680,000,000 cubic feet of water are conveyed from 

 the Gulf per hour, or 133,816,320,000,000 cubic feet daily.^ Conse- 

 quently the total quantity of heat transferred from the equatorial regions 

 per day by the stream amounts to 154,959,300,000,000,000,000 foot- 

 pounds. From observations made by Sir John Herschel and by M. 

 Pouillet on the direct heat of the sun, it is found that were no heat 

 absorbed by the atmosphere, about 83 foot-pounds per second would 

 fall upon a square foot of surface placed at right angles to the sun's 

 rays.^ Mr. Meech estimates that the quantity of heat cut off by the 

 atmosphere is equal to about 22 per cent, of the total amount re- 

 ceived from the sun. M. Pouillet estimates the loss at 24 per cent. 

 Taking the former estimate, 64* 74 foot-pounds per second will there- 

 fore be the quantity of heat falling on a square foot of the earth's 

 surface when the sun is in the zenith. And were the sun to remain 

 stationary in the zenith for twelve hours, 2,796,768 foot-pounds 

 would fall upon the surface. 



It can be shown that the total amount of heat received upon a 

 unit-surface on the equator during the twelve hours from sunrise 

 till sunset at the time of the equinoxes is to the total amount which 

 would be received upon that surface, were the sun to remain in ihe 

 zenith during those twelve hours, as the diameter of a circle to half 

 its circumference, or as 1 to 1-5708. It follows, therefore, that a 

 square foot of surface on the equator receives from the sun at the 

 time of the equinoxes 1,780,474 foot-pounds daily, and a square mile 

 49,636,750,000,000 foot-pounds daily. But this amounts to only 

 3",TTT,TT"o PS'^^ of 'tlie quantity of heat daily conveyed from the tropics 

 by the Gulf-stream. In other words, the Gulf-stream conveys as 

 much heat as is received from the sun by 3,121,870 square miles of 

 surface at the equator. The amount thus conveyed is equal to all 

 the heat which falls within 63 miles on each side of the equator. 

 According to calculations made by Mr. Meech,'' the annual quantity 



1 Phil. Mag. for February 1867, p. 127. 



^ Captain Maury considers the Gulf-stream equal to a sti-eam 32 miles broad and 

 1200 feet deep, flawing at the rate of five knots (.•^8,41.5 feet) an hour (Physical Geo- 

 graphy of the Sea, § 24). This gives 6,166,700,000,000 cubic feet per hour as the 

 quantity of water conveyed by this stream. Sir John's Herscbel's estimate is still 

 greater. He considers it equal to a stream 30 miles broad and 2200 feet deep, flowing 

 at the rate of four miles an hour (Physical Geography, \ 54). This makes the quan- 

 tity 7,359,900,000,000 cubic feet per hour. Sir John estimates the temperature at 

 86° F. 



3 Trans, of Royal Soc. of Edin., Vol. xsi., p. 57- Phil. Mag. S. 4, Vol. ix. p. 36. 



* Smithsonian Contributions to Knowledge, Vol. IX. 



