92 COMPARISON OF BAROMETERS. 
Captain Gunnison’s barometers compared with the standard barometer of Dr. G. Engelmann, St. Louis, 
June 4 to 9, 1853. 
Ten observations were made— 5 
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. 
Bunten, No. 551=E—0."0212  ,,, : 
Bunten, No. 551—E-F0."027 $ —0."048, difference of range. 
Bunten, No. 496=E+0."0462__,, i 
Ponten, No. oc E EAR —0."063, difference of range. 
Aneroid, No. 9889—E —0."055 js 
Ancroid, No. 9889=E+6. Guo $ —0."090, difference of range. 
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ee ee 
E. represents Engelmann’s standard barometer. 
Both of Bunten’s barometers are very slow in their movements. B. 551 gives a very dull 
sound when the tube is reversed, indicating air in the tube; 496 gives a clearer sound, and is 
probably free of air. 
The station of Dr. Engelmann’s barometer is above low-water mark of the Mississippi 106.5 
feet, and above the Gulf of Mexico 482 feet. 
Barometer Engelmann was, in June, 1853, equal to— _ 
Bunten, No. 551—0."006 
Bunten, No. 496—0."080 
The Aneroids were both set to correspond exactly with barometer E. 
After the voyage to California and back, barometer Engelmann was found, in September, 1854, 
equal to— 
Bunten, No. 551—0."072 
Bunten, No. 496+0.”116 
Aneroid, No. 7889 —0."448 
Aneroid, No. 9293+0.”263 
Therefore, as barometer E. has remained unaltered— 
Barometer Bunten, 551, is now higher by 0.066 than 14 tacita ago. 
e 496, is now lower by 0.7196 5 
Aneroid, 7889, is now higher by 0.”448 E e 
* 9293, is now lower by 0.7263 " " 
Bunten, 551, is by far the best instrument of the whole set; but both barometers have the 
inside of the tubes at the lower as wellas the upper levels so much soiled and darkened by 
oxydized mercury, that at a certain elevation of the barometer, at least, the reading off becomes 
very difficult if not ccm 
