184 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Weight of 188 c. c. moist air at 17°.3 and 74.4 cm. 

 Observed loss of weight of globe 



= .22 grm. 

 = 1.39 " 



Water displaced by difference of volume = 1.61 " 



Diff. of volume corresponding to 74.4 cm. pressure = 1.61 c. c. 

 " " 76.8 cm* " =1.66c.c. 



Weight of 1.66 c. c. of air at 76 cm. and 22° C* = 1.98 mg. 



Below are given the data of the two series of determinations which 

 were made. 



Number. 

 1. 



2. 

 3. 

 4. 

 5. 



Loss of Weight. 

 Grams. 



1.34 

 1.39 

 1.39 

 1.37 

 1.39 



Series I. 



Atmospheric Pressure. 

 Centimeters. 



76.40 

 75.86 

 75.80 

 75.78 

 75.75 



Temperature. 

 °C. 



18.10 

 17.30 

 17.32 

 17.40 

 17.45 



Correction. 



Milligrams. 



1.92 

 1.98 

 1.98 

 1.96 

 1.99 



1.99 



Total average, 1.98 milligrams. 



The quantity 1.98 milligrams is then the correction sought, and 

 this closely agrees with Lord Rayleigh's estimate of the value in the 

 letter above referred to. Since in the work described in the preceding 

 paper all the data required for the calculation were not recorded in 

 every case, it will be impossible to apply this correction to each deter- 

 mination separately. But no sensible error can result if we add the 

 correction to the average apparent weight of the hydrogen, easily cal- 

 culated from the data given in the table on page 173. 



* 22°C. and 76 cm. pressure were the average atmospheric conditions at the 

 times of weighing the globe in the previous determinations, and 76.8 cm. was 

 the average difference of the pressure on the globe when exhausted and full of 

 hydrogen. 



