THE EQUIPMENT 



37 



pass reads in "points" and not degrees. As each 

 man finishes his two-hour trick at the wheel, he 

 calls out to his reliever: "East by south half south," 

 and not "107 degrees." 



On one side of the wheel, mounted near the rail, 

 stands the rain-gauge; and on the other, the evap- 

 orimeter. The latter is made of glass, and is used 

 to measure the rate of evaporation of sea-water 

 from day to day. This subject is part of the 

 general investigations made of the influence on cli- 

 mate of movements of large bodies of warm or 

 cold water. We wished to study the transfer of 

 heat between the sea and the atmosphere; and 

 the evaporimeter, together with the electric resist- 

 ance-thermometers, gave us much needed infor- 

 mation. 



On the taffrail around the stern is the auto- 

 matic recorder for the potential gradient of the 

 atmosphere's electricity. The negative charge on 

 the Earth's surface causes an electric pressure in 

 the air increasing with height above the Earth's 

 surface. Ordinarily this rate of increase or gradi- 

 ent is in the neighborhood of one hundred volts 

 per meter near sea-level. There are daily vari- 

 ations, aside from the local changes due to dis- 

 turbances in the atmosphere near the ship. We 

 have already referred to the mysterious surge in 

 the potential gradient which occurs simultane- 

 ously over the whole Earth. It was discovered 

 after examining observations obtained on previous 

 cruises of the Carnegie, and our aim was now to 

 collect records from widely separated geographical 



51 



J? 



5J 



Ji 



A RiCHTER AND WiESE DeEP-SEA ReVERSING-THERMOMETER 



Protected against pressures encountered in the depths of the ocean — (A) Sea-water 

 thermometer, (B) auxihary thermometer for making correction for air-temperature on 

 deck, (C) point at which mercury-capillary breaks on reversal, (D) mercury-shield which 

 protects bulb from pressure of sea. 



