358 COMPUTATION OF ALTITUDES. 
abnormal corrections, 
No instrument error is given, so the index reading has been assumed 
as correct. 
After being corrected as above, the altitudes were calculated by the tables of Mr. Guyot, 
the process being somewhat shortened by the method of preparation. 
The following example will show the method of computing these observations, as also the 
observations of Lint from Fort Benton across Lewis and Ulark’s Pass. 
EXAMPLE. 
Data for determining the altitude of Birch river, in the mountains, by three observations. 
Date. Hour. | No.of ba- | Reading of | Attached ther- | Detached ther- 
\ rometer. | barometer. mometer. mometer. 
^79 o 
May 21,1804 ......-5 5 2 p. m... 2 25. 374 76 74 
Мау 931906 „аана 9р. m 25. 834 58 53 
May. 22, 1864 ioe Sunrise 25. 374 54 52 
Corrections applied before computation. 
2 p. m., May 21. | 9 p. m., May 21. |Sunrise, May 22. 
Barometric reading 25. 374 25. 834 25. 374 
Correction to reduce to 32° Fahrenheit. . — 108 — 057 — 058 
Correction for index error 000 000 000 
Correction for horary oscillations........ Table B, 4 .020 + 008 — 020 
Correction for abnormal oscillations. .... Table D, + .062 + 076 + 061 
Corrected readings............-.| 25, 348 25. 861 25. 357 
Mean of corrected readings, 25, 522 ; mean temperature, 67 
Computation by Guyot’ s tables. 
H ші 306.054 «n dvs 
22: 25.0629 Ce em e 
Table I gives for Н = 30.057.... 
| osecevess T 64 
«ээле етее e TFS 61 
eevee paie dvs а оао dV 28762.4 
Table I gives for Н/ = 25.522.................. ӨӨӨ 24479.4 
Approximate difference of level Р.................. 4273.0 
D x (T +T —64) — 4273 x 67 
254 = mm 5-5... voi» vesetere, Te 816,10 
Second approximate difference D’ ............... 
4. 4591.10 
Table ІП gives for D' = 4591.10, Lat. 48° 10'........... -- 1.30 
Table IV gives for: D' zz 4591.10 «9... ere ae veh ЛӘ, В 
Altitude of station, in feet .4...........ш..шшвш"..... 
