276 Mr. J. Croll on the Physical Cause of Ocean-currents. 



Mr. Findlay rose to make some observations, and, among other 

 things, made the following remarks : — 



" When, by the direction of the United States Government 

 ten or eleven years ago, the narrowest part of the Gulf-stream 

 was examined, figures were obtained which shut out all idea of 

 its ever reaching our shores as a heat-bearing current. In the 

 narrowest part, certainly not more than from 250 to 300 cubic 

 miles of water pass per diem. Six months afterwards that water 

 reaches the banks of Newfoundland, and nine or twelve months 

 afterwards the coast of England, by which time it is popularly 

 supposed to cover an area of 1,500,000 square miles. The pro- 

 portion of the water that passes through the Gulf of Florida 

 will not make a layer of water more than 6 inches thick per 

 diem over such a space. Every one knows how soon a cup 

 of tea cools ; and yet it is commonly imagined that a film of 

 only a few inches in depth, after the lapse of so long a time, 

 has an effect upon our climate. There is no need for calcu- 

 lations; the thing is self-evident/' 



About two years ago Mr. Findlay objected to the conclusions 

 which I had arrived at regarding the enormous heating-power 

 of the Gulf-stream on the ground that I had overestimated 

 the volume of the stream. He stated that its volume was only 

 about the half of what I had estimated it to be. To obviate 

 this objection in future, in my last paper on the heating- 

 power of the stream, published in the February Number of the 

 Philosophical Magazine for 1870, I reduced the volume to one 

 half of my former estimate. But taking the volume at this low 

 estimate, it was nevertheless found that the quantity of heat 

 conveyed into the Atlantic through the straits of Florida by 

 means of the stream was equal to about one fourth of all the 

 heat received from the sun by the Atlantic from the latitude of 

 the Strait of Florida up to the Arctic Circle. 



Mr. Findlay, in his paper read before the British Association, 

 stated that the volume of the stream is somewhere from 294 to 

 333 cubic miles per day ; but in his remarks made at the close 

 of Dr. Carpenter's address, he states it to be not greater than 

 from 250 to 300 cubic miles per day. I am unable to recon- 

 cile any of those figures with the data from which he appears 

 to have derived them. He stated in his paper to the British 

 Association that " the Gulf-stream at its outset is not more than 

 39J miles wide, and 1200 feet deep." " From all attainable 

 data," he says, " he computes the mean annual rate of motion to 

 be 65*4 miles per day ; but as the rate decreases with the depth, 

 the mean velocity of the whole mass does not exceed 49*4 miles 

 per day. But when he speaks of the mean velocity of the Gulf- 

 stream being so and so, he must refer to the mean velocity at 



