132 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



February 28, 1902. Ice in Bath at 12.30 p. m. Pure previously Boiled 



Freezing Water run in in Place of Ice-Water at 2.00 p.m. 



Meniscus ahove the Point. 



Hour 



Temperature of barometer < 



McLeod gauge with corre- < 

 sponding pressures . . ' 



Reading of cross-hair set I 

 on meniscus .... I 



Revolutions of dial* . . 



Reading of cross-hair set i 

 on point ' 



Distance between menis- 

 cus and point .... 



Corrected excess of pres- 

 sure of gas over height 

 of iron rod 



°C (upper) 

 °C (lower) 



dial divisions 

 millimeters 



dial number 



dial number 



dial divisions 

 millimeters 



millimeters 



Successive Readings. 



2.15 



20.0 

 20.0 



320 

 0.041 



32.6 

 32.(5 

 32.5 



35.4 

 35.6 

 35.6 



103.0 

 1.269 



1.310 



2.40 



20.0 

 20.0 



308 

 0.038 



48.4 



48.3 

 48.5 



0.9 

 1.2 

 1.2 



102.5 

 1.263 



1.301 



3.05 



20.0 

 20.0 



267 

 0.033 



38.7 

 38.9 

 38.9 



42.3 

 42.5 



42.7 



103.7 



1.278 



1.311 



3.50 



20.0 

 19.9 



250 

 0.032 



44.3 

 44.1 

 44.5 



47.5 

 47.8 

 47.5 



103.3 

 1.273 



1.305 



4.20 



20.0 

 20.0 



250 

 0.031 



4.0 



3.8 

 4.0 



7.7 

 7.7 



103.8 

 1.279 



1.310 



Average 1.307 ± 0.001 mm. 



Because the iron rod was 761.34 mm. long, the total height of mer- 

 cury at 20° supported by the gas pressure was 762.647 millimeters. 

 The points a and a 1 being essentially on the same level, this is also es- 

 sentially the pressure of the gas iu the bulb. Each determination of the 

 coefficient of expansion yielded a corresponding table at 0°, and another 

 similar one at 32.48°. The difference between the corrected values for 

 the two temperatures is recorded in the tables on pp. 136, 139 as p. 



A change in atmospheric pressure affects equally the levels of the 

 mercury in the lower and in the upper part of the Lord Rayleigh ba- 

 rometer. Provided, however, that the pressure on the lower meniscus, 

 fixed by the pressure in the side tube of the bulb, did not alter, a re- 



* One revolution of the dial equals fifty dial divisions. 



