VOL. LXVII.] PHILOSOPHICAL TKANSACTtONS. 235 



zero, expressed in grains, was called the air in experiment. The apparent expan- 

 sion of that air was measured by the grains that filled the several sections of the 

 tube between zero and the boiling point; the sum being the total expansion or 

 increase of volume, from a heat of 212°. The apparent expansion, thus 

 found, was again augmented for the dilatation of the tube, on the following 

 principles. 



In the first part of this paper I have shown, that solid glass rods dilate much 

 less than barometer tubes. The mean between Mr. Smeaton's and my experi- 

 ments, gives -rrrTTo of 3n inch for the longitudinal extension of every foot of 

 these tubes, by 212°. From the rate of going of a clock, for near a year, whose 

 pendulum rod is solid glass, its dilatation seems to be J- part of a steel rod, or 

 ^ ^!'^'^ ^ on a foot, by 212°. Now as the manometers resemble solid rods much 

 more than they do barometer tubes, it is probable that their dilatation, even al- 

 lowing for the greater extension of the bulb, would not exceed t-ot-o of ^i '•^ch 

 on a foot, or -pott-o- P^^t on every 2 inches. In this ratio I have therefore aug- 

 mented the apparent, to obtain the true, capacity of each manometer. The 

 equation, amounting to about -^-^ part of the whole, being less than the com- 

 mon error of such complicated observations, might in fact have been entirely 

 omitted, without producing any material alteration in the results. 



Having in this manner computed the total increased volume of any number 

 of equal parts of air, according to the capacity of the bulb and tube in grains, 

 and very often likewise the partial expansions for intermediate temperatures, ex- 

 pressed by the contents of the corresponding sections of the tube, I then found 

 the ratio answering to 1000 equal parts, which, being divided by the degrees of 

 difference of temperature, gave the mean rate for the whole scale, or the parti- 

 cular rate for any intermediate section of it. 



The experiments, considered in this way, are distributed into 4 classes, of 

 which the results are comprehended in 4 tables. The first shows the expansion 

 of air, whose density was much greater than that of the common atmosphere. 

 The 2d, which was divided into 2 sets, contains those on air that sustained a 

 pressure less than the atmosphere. In the 3d class, a very short column of 

 quicksilver being employed to confine the air, its density differed little from that 

 we commonly breathe in : this class was likewise subdivided into 2 sets. The 

 4th and last class of experiments were made on air of the common density, arti- 

 ficially moistened by the admission, sometimes of steam, and at others of water, 

 into the bulb; it is accordingly distinguished into 2 sets. 



From the experiments of the 1st class it appears, that 1000 equal parts of 

 common air, loaded with 2i atmospheres, being affected with a heat of 212'^, 

 expands 434 of those parts ; that is, in its dilated state, it occupies a space bearing, 

 to that which it originally filled, the proportion of 1434 to 1000: hence the 



H H 2 



