94 Mr. J. Croll on Ocean-currents in relation to 



We may, therefore, in this case conclude that 59° of rise is 

 probably not very far from the truth as representing the influ- 

 ence of the Gulf-stream. The Gulf-stream, instead of producing 

 little or no effect, produces an effect far greater than is gene- 

 rally supposed. 



Our island has a mean annual temperature of about 12° above 

 the normal due to its latitude. This excess of temperature has 

 been justly attributed to the influence of the Gulf-stream. But 

 it is singular how this excess should have been taken as the 

 measure of the rise resulting from the influence of the stream. 

 These figures only represent the number of degrees that the 

 mean normal temperature of our island stands above what is 

 called the normal temperature of the latitude. 



The way Professor Dove constructed his Tables of normal tem- 

 perature was as follows : — He took the temperature of thirty- 

 six equidistant points on every ten degrees of latitude. The 

 mean temperature of these thirty-six points he calls in each case 

 the normal temperature of the parallel. The excess above the 

 normal merely represents how much the stream raises our tem- 

 perature above the mean of all places on the same latitude, but 

 it affords us no information regarding the absolute rise pro- 

 duced. In the Pacific, as well as in the Atlantic, there are im- 

 mense masses of water flowing from the tropical to the tempe- 

 rate regions. Now, unless we know how much of the normal 

 temperature of a latitude is due to ocean-currents, and how much 

 to the direct heat of the sun, we could not possibly, from Pro- 

 fessor Dove's Tables, form the most distant conjecture as to how 

 much of our temperature is derived from the Gulf-stream. The 

 overlooking of this fact has led to a general misconception re- 

 garding the positive influence of the Gulf-stream on tempera- 

 ture. The 12° marked in Tables of normal temperature do not 

 represent the absolute effect of the stream, but merely how 

 much the stream raises the temperature of our country above 

 the mean of all places on the same latitude. Other places have 

 their temperature raised by ocean-currents as well as this country; 

 only the Gulf-stream produces a rise of several degrees over and 

 above that produced by other streams in the same latitude. 



At present there is a difference merely of 80° between the 

 mean temperature of the equator and the poles*; but were each 

 part of the globe's surface to depend alone upon the direct heat 

 which it receives from the sun, there ought, according to theory, 

 to be a difference of more than 200°. The annual quantity of 



* The mean temperature of the equator, according to Dove, is 79°'/, 

 and that of the north pole 2 0, 3. But as there is of course some uncertainty- 

 regarding the actual mean temperature of the poles, we may take the dif- 

 ference in round numbers at 80°. 



