12 PROCEEDINGS OF THE AMERICAN ACADEMY 



merely as a satisfactory and important check upon the further results 

 of that series. The equation deduced from this latter series, I regard 

 as best representing my measurements on dry air. It will be noticed, 

 on comparing the two series, that the greatest deviation of the two 

 series is at 100°, where it amounts to less than 0.4 per cent. 



Measurements 1 and 2 were taken during preliminary trials of the 

 apparatus. In 3 to 8 the first capillary was in boiling water, 

 the second in ice, this reversal of the usual sequence of tempera- 

 tures being made in order to test the apparatus. The mean of these 

 five measurements (the sixth having been rejected when made, as 

 having been taken before the static condition of the process was 

 reached) gives 



y — Vm — 1.267 ± a.d. 0.002. 

 The above equation gives for t = 99°. 94 



^= 1.2666, 



Vo 



and the direct observation made, as were all those from which the 

 equation is derived, with the first capillary at 0°, gives as the mean 

 at 99°. 66 



^= 1.2666. 



'70 



The close agreement of these numbers seems to indicate a freedom 

 from constant error of any considerable magnitude in the value of K 

 and in the expansion correction to this value. 



Fifth Series. April, 1880. — This series was taken with the appa- 

 ratus as described at page 2, immediately after the completion of the 

 second series with carbonic acid. The measurements were made 

 under as favorable conditions as any of this paper, and are of greater 

 weight than all of the others upon air. The full data for the compu- 

 tation of these results are given in Table IV. in such form that a 

 recomputation, in so far as relates to those portions subject to possible 

 modification of such amount as to materially change the result, may 

 at any time be made. The value of K used was the same as that 

 used for the second series of carbonic acid. 



These measurements may be divided according to temperatures 

 into six groups, and are very concordant except that the sixth group 

 shows a deviation of about 0.6 per cent from the value which the 

 other five groups would indicate at that temperature. There appears 



