74 BAROMETERS COMPARED. 
CAPTAIN GUNNISON’S BAROMETERS COMPARED WITH THE STANDARD BAROMETERS OF DR. ENGEL- 
MANN. 
Sr. Lours, June 4 to 9, 1853. 
Ten observations were made. 
Range of standard barometer in that period from 29.505 to 29.748. Range 0”.243. 
Mean differences of standard and compared barometers. 
Bunten, No. 551— E + 0".006. Bunten, No. 496 — E + 0".080 
Aneroid, No. 9889 = E — 0".015. Aneroid, No. 9293 = E — 0".025 
Extreme differences of range of standard and compared barometers. 
nexis qid T es : à MES ? = 0".048, range of difference. 
Bunten, No. 496 = m s zà 0".046 
Do. 0".109 
Le = 0".063, range of difference. 
Aneroid, No. 9889 = = E — M^ 055 hes 
Do. 
0.035 0".090, range of difference. 
Aneroid, No. 9293 = = u 0".005 
Do. 0".045 
E. represents Engelmann's ae barometer. 
Both Bunten barometers are very slow in their movements. B. No. 551 gives a very dull 
sound when the tube is reversed, indicating air in the tube. No. 496 gives a clear sound, and 
is probably free of air. 
The station of Dr. Engelmann’s barometer is above low-water mark of the Mississippi 106.5, 
and above the Gulf of Mexico 482 feet. 
Bar. Engelmann was in June, 1853, equal to— 
Bunten, No. 551 — 0".006 
Do. No. 496 — 0".080 
The Aneroids were both set to correspond exactly with bar. E. 
After the voyage to California and back, bar. Engelmann was found in September, 1854, 
equal to— 
= 0".040, range of difference. 
Bunten, No. 551 — 0".072 
Do. No. 496 + 0".116 
sciam No. 7889 — 0".448 
No. 9293 + 0".263 
Therefore, as bar. E. has remained unaltered, 
Bar. Bunten No. 551 is now higher by 07.066 than 14 months ago. 
0. No. 496 is now lower by 0".196 id 
Bar. Aneroid No. 7889 is now higher by 0".448 Ys " 
Do. No. 9293 is now lower by 0".263 i zm 
Bunten No. 551 is by far the best instrument of the whole set; but both barometers have the 
sides of the tubes at the lower as well as the upper levels so much soiled and darkened by 
oxydized mercury, that at a certain elevation of the barometer, at least, the reading becomes 
very difficult, if not impossible. 
The iitireida are certainly very unreliable; but within the limited range of my observations, 
(between 29 and 30 inches,) they per PME well and corresponded pretty accurately with the 
changes of my own barometer. 
In calculating elevations from barometrical data, it seems best not to compare isolated obser- 
vations made on the same day or at the same hour; but to refer the observations made in the 
