PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 577 



that the indicator was invented by an ingenious young clerk in the 

 employ of Watts, at the Soho factory, where Watts' steam engines 

 were constructed. 



J. Stanley Grimes, Esq., addressed the Association as follows on 



THE GREAT 0CEAN CURRENTS, AND THE FORCES THAT 

 REGULATE THUM. 



It is now admitted by the best authorities that the cause of 

 the great and constant ocean currents is the diflerence of tempera- 

 ture between the higher and the lower latitudes. The water, being 

 heated near the equator, expands and overflows north and south 

 toward the poles, constituting a surface current, the water of which, 

 as it gradually cools, condenses and sinks until it becomes of the 

 same temperature as the polar waters. A large quantity of water 

 is also evaporated in the equatorial regions and carried poleward, 

 probably from five to thirty degrees of latitude, before it falls 

 again into the ocean ; even then it is warm and fresh, and adds to 

 the surface current that flows poleward. The loss of so much 

 water in the equatorial region is compensated by the cold under- 

 currents that flow from the polar regions. We thus have a perfect 

 explanation of the fact that an interchange of cold and Avarm cur- 

 rents is continually going on between the equatorial and the polar 

 zones of the earth. 



At the first thought we should suppose that these two currents 

 would flow, one due south and the other due north ; but the truth 

 is that they are deflected eastward when moving toAvard the pole, 

 and westAvard when moving toward the equator. The reason of 

 this fact is now of so much importance that, although it has been 

 stated by many authors, and may be aa'cU understood by most of 

 my readers, I shall, notAvithstanding, endeavor to explain it as 

 clearly as possible, for the benefit of those to Avhom the subject is 

 not familiar. 



Effect of the Earth's Eotation upon the Ocean Currents, 

 so far as it has Hitherto been Understood. 



The poles of the earth are relatively immovable, AA'hile each spot 

 at the equator is moving eastward about one thousand miles an 

 hour around the earth's axis. The nearer Avater, or anything else, 

 is to the equator, the farther eastward it moves in a given time ; 

 and, on the contrary, the nearer the pole it is, the less is the dis- 

 tance which it travels eastward in the same time. Of course, each 

 degree of latitude has its own rate of easterly velocity. This Avill 



[Am. Inst. J KK 



