304 Captain Sabine’s comparison of barometrical and 
produced its former correspondence between the barometers, 
but that previously to that period, and when the mercury 
has been supposed to have been, as described, slightly con- 
cave in the tube of Jones’s, its indications with the additive 
of -f-.ic)6, would be uniformly too high for the agreement ; 
as much so on the average as .0105, or one-hundredth of an 
inch nearly. I have considered it preferable, therefore, to 
employ -J-.1845 as the index correction on the 21st instant, 
instead of -f.i 96 , as it was the difference actually observed 
by direct comparison on the same afternoon, and, as far as 
can be judged, under similar circumstances : the result, how- 
ever, has been computed on both suppositions, and is inserted. 
No such uncertainty exists in any of the previous observ- 
ations, as, on all the former occasions, the mercury in both 
barometers presented a more or less convex surface. 
In the following table the actual readings are given as be- 
fore, reduced to the temperature of 32 0 for the expansion 
of mercury, and the scale ; and the last column shows the 
index correction required in each 
comparison to produce an 
agreement. 
Newman’s. 
Jones’s. 
Index correction. 
July 21. 6 P.M. 
29.311 
29.259 
.184“' 
— 10 P.M. 
29.314 
29.262 
.184 
— 12 P.M. 
29.312 
29.259 
.186 
22. 3 A.M. 
29.306 
29.253 
.186 
^.1845 
— 3.50 A.M. 
29.303 
29.253 
.183 
— 5.00 A.M. 
29.294 
29.244 
.183 
— 7.30 A.M. 
29.303 
29.250 
. 86J 
— 12 Noon. 
29.360 
29.295 
• 195 ~] 
— 1.30 P.M. 
29.367 
29.302 
.194 
> .195 
— 2.30 P.M. 
29.373 
29.310 
.194 j 
(Foster obs.) — 2.45 P.M. 
29.383 
29.316 
• 197 J 
