ON MIXlED SASES. H 



posed to water, will expand more than that which is kept dry. Examination of 

 provided the corresponding augmentations of their tempera- ^^- Walton's 

 tures be equal ; which phenomenon is thus explained on the ed gases. 

 principles of the theory. The vapour that arises from the 

 sides of the wet tube, possesses a spring of its own; therefore- 

 it takes off part of the weight of the mercury from the air, and 

 thereby leaves it to expand itself, so as to re-adjust the equi- 

 librium. According to this explanation, if / and g represent 

 the length of the columns of dry and moist air at any tempe- 

 rature; and if c denote the length of a column of mercury, 

 equal in weight to the pressure that confines the contents of 

 the tubes ; and if/ be put for the spring of va,pour of the 

 same temperature measured by a column of mercury, we have 



Ic fS ^ 



g-=. from which we also get c= 



c-f; g-l 



the last expression affords us an opportunity of comparing 

 the preceding explanation, and therefore the theory itself with 

 facts; for, according to the experiments of Mr. Schmidt, 

 ioOO parts of dry air at 32 degrees of Farenheit, will expand 

 to 1087,11 parts, by being raised to 59 degrees, in contact 

 with water; call this nurnber^: according to (he same author* 

 1000 parts of dry air at 32 degrees will expand to 1053,61 

 parts, by being heated to 59 degrees in a dry tube; let this 

 number be /; then g — /= 33.50: but/, or the spring of 

 vapour at 59 degrees, is .507, according to Mr. Dalton ; then 

 ^ = 551,164; hence c = 16,15 inches; which expresses 

 the height of the barometer, together with the column of mer- 

 cury contained in the tube. If the temperature be stated at 

 95 degrees, c will amount to little more than 8 inches : now 

 it is highly improbable that Mr. Schmidt made his experiments 

 when the barometer stood at a height indicated by either of 

 these numbers. — This application of the theory to practice, 

 affords a presumptive evidence that the principles of it are not 

 altogether just, supposing the experiments of Mr. Dalton and 

 Mr. Schmidt to be correct : but a positive proof of a want of 

 accuracy in these principles may be obtained by introducing a 

 small change into the manner of conducting the experiment 

 made with moist air. This alteration consists in discarding the 

 stopple of mercury, and substituting the simple pressure of the 



