142 LIGHT SCIENCE FOR LEISURE HOURS. 



He held that the Gulf Stream is formed by the outflow 

 of waters which have been forced into the Caribbean 

 Sea by the trade-winds ; so that the pressure of these 

 winds on the Atlantic Ocean forms, according to Dr. 

 Franklin, the true motive power of the Gulf-Stream 

 machinery. According to Maury, this theory has 

 " come to be the most generally-received opinion in the 

 mind of seafaring people." It supplies a moving force 

 of undoubted efficiency. "We know that, as the trade- 

 winds travel toward the equator, they lose their west- 

 erly motion. It is reasonable to suppose that this is 

 caused by friction against the surface of the ocean, to 

 which, therefore, a corresponding westerly motion must 

 have been imparted. 



There is a simplicity about Franklin's theory which 

 commends it favorably to our consideration. But 

 when we examine it somewhat more closely, several 

 very decided flaws present themselves to our attention. 



Consider, in the first place, the enormous mass of 

 water moved by the supposed agency of the winds. 

 Air has a weight volume for volume which is less 

 than one eight-hundredth part of that of water. So 

 that, to create a water-current, an air-current more 

 than eight hundred times as large and of equal velocity 

 must expend the whole of its motion. JSTow, the trade- 

 winds are gentle winds, their velocity scarcely exceed- 

 ing in general that of the more swiftly-moving portions 

 of the Gulf Stream. But even assigning to them a 



