186 



"Experiments 

 ayj3.vn*t the 

 *wstence of a 

 aqueous at 

 jsac&puere. 



Attrition to 

 aMjcwtia: ne- 

 cessary.. 



ON THE EXPANSION OF MOIST Al*lt. 



water into it. The seolipile was then removed from the pan, 

 the aperture being covered by the ringer of the operator. 

 After being carefully wiped with dry clothes, it was weighed, 

 and found to contain 185 grain measures of air, which was 

 evidently saturated with moisture, and at the temperature 

 of 64°. But 53 measures of air thus circumstanced contain 

 52 measures of dry air. Thus it appears, that 181*5 mea- 

 sures of dry air at 64° occupy 2895 such measures when 

 raised to 212° in contact with water of the same temperature: 

 whence it follows, that I measure of dry air dilates so as to 

 become equal to 15*^5 measures in similar circumstances. 

 It is proper to observe, that the barometer stood at 29*66 

 at the time; and that the height of the water in the pan, 

 reckoning from the mouth of the aeolipile, increased the 

 pressure to 29*90 : therefore the true dilation of one mea- 

 sure amounts to 16*70. But one measure of dry air at 

 64° occupies no more than 0*93344 parts of a measure when 

 cooled to 32°; therefore the whole bulk of one measure of dry 

 air raifed from 32° to 212° in contact with water may be 

 stated at 17*100 measures. 



I have made several experiments both with this aeolipile 

 and a glass flask on air of 64°, which was raised to tempera- 

 tures less than 212*, but the results did not correspond to 

 the theorem given in the Manchester Memoirs for the 

 purpose of finding the dilatation of moist gasses confined in 

 the manometer. Does not then the evidence of direct ex- 

 periments authorize us to say, that the existence of an aque- 

 ous atmosphere is not proved? or more properly does not the 

 same evidence show this imperceptible fluid to be not only 

 invisible, but also imaginary ? 



Some of your readers may think the preceding experi- 

 ments are related too minutely, particularly the first and 

 third; but should an impartial person wish to repeat them, 

 he will be of a different opinion. In fact too much precau- 

 tion cannot be used to prevent the manometer or aeolipile 

 from touching the bottom of the boiler ; for if this be not 

 done, the experiment will fail, as I have found on different 

 occasions ; and this has happened when the water in the pan 

 did not boil. I should also recommend a wide cylindrical 

 boiler in preference to a small vessel with a long narrow 



neck 



