I9I4-] 



ATMOSPHERIC PRESSURE. 



63 



single air-pressure were not so good as those obtained at normal 

 atmospheric pressure in the open air outside the tank, with a larger 

 fork radius, and free air-space. That is, the curves of linear con- 

 vection against wind-velocity, on logarithm paper, showed more 

 tendenc}- to deviate from a straight line, in these tank tests than in 

 open-room tests, both at low speeds and at high speeds. These 

 deviations might perhaps be explained by air-churnings in the tank, 

 due to the motion of the fork and wire in a somewhat confined 

 space. 



The insulated wires leading to motor, magneto, and test-wire, 

 were brought out through holes in a wooden plug bolted air-tight 

 over a manhole. 



The speed of rotation of the motor inside the tank was measured 

 in two independent ways; namely (i) by the e.m.f. of the little 

 magneto-generator coupled to the motor, (2) by a contact made 



^L 90 

 86 



fi^-l'^ ■ ■ ■ 



..7Z 

 ZS- 



a 



.._ 70 . .2.0.. .30....^. S.0 . ifC . IO...W BS .160. a-_ 



_:,.i ___, Temppriii<if^ °.C \ 1 i. ; i^- 



::h;::llK.Hii:)i:i!l.niiH:ii:iiilHi.it!i;lii!iiinil:i:iiUiaia;iti!it: imM;il:;t!iuiili.iiliiulMtitui 



Fig. 6. Resistance in oil of 550 cm. of the Platinum Test Wire at dif- 

 ferent temperatures between 0° C. and 97° C. in order to determine the 

 resistivity temperature-coefficient. 



through a wire on the motor shaft once in each revolution, which 

 gave a click in a telephone. The speed calibration of the magneto 

 and its voltmeter could thus be checked, from time to time, by count- 

 ing the telephonic clicks in one minute. 



