I9I4] 



ATMOSPHERIC PRESSURE. 



65 



TABLE II. 



Series of Measurements on February 16, 191 1. Observers A. E. K. and 

 H. S. S. Pressure in tank 75.2 cm. Hg above that in room. Barometer 

 778 mm. at 14.5° C. Temp, air in tank 18.5° C. Mean absolute pressure 

 in tank 2.04 megabars. Res. of test platinum wire between pressure wires 

 kept at 8.44 ohms. Inferred temp, elevation 391.5° C. R. P. M. of driving 

 motor =r 1.14 X magneto voltage. 



Column I gives the voltage generated by the magneto on the 

 driving-motor shaft. From these readings, the speed of the test- 

 wire through the air in the tank; or the "wind-velocity" v of 

 Column II is directly derived in cm. per sec. Column III gives, at 

 each steady speed, the P.D. between pressure wires in C.G.S. mag- 

 netic absolute units or " abvolts." Column IV gives the correspond- 

 ing current strength in C.G.S. magnetic absolute units or " absam- 

 peres." The ratio E/I is approximately constant at 8.44 X 10^ 

 absohms, or 8.44 ohms. Column V gives the linear dissipation of 

 heat from the wire, or the abwatts (ergs per second) per cm. of 

 wire length. Column VI gives this linear dissipation per deg. Cent, 

 of inferred temperature elevation. It will be seen that this varies 

 from 1.05 X 10* abwatts per cm. and ° C. at standstill, up to 9.075 X 

 10^ at 2,166 cm. per sec. Column VII gives the entries of VI 

 divided by V^ giving a value nearly uniform about 1,960, until the 

 velocity v falls to 300 cm. per sec. At standstill, of course, owing 



PROC. AMER. PHIL. SOC. LIII, 2I3, E, PRINTED JUNE I9, I914. 



