DETERMINATION OF ALTITUDES BY BAROMETER 
125 
Eesults obtained by computation —Continued. 
Date. 
Station. 
Hour. 
Altitude by barometer above depot camp, 
computed by— 
Differences between altitudes determined 
by barometer and spirit level. 
Old method, using 
Lee’s tables. 
New method, using 
observed air tem¬ 
peratures. 
New method, using 
mean daily air 
temperatures. 
Old method, using 
Lee’s tables. 
New method, using 
observed air tem¬ 
peratures. 
New method, using 
mean daily air 
temperatures. 
1853. 
h. m. 
Feet. 
Feet. 
Feet. 
Feet. 
Feet. 
Feet. 
Oct. 
2 
53 
12. 00 m. 
1937. 9 
1911. 7 
1884.7 
— 28.2 
— 2.0 
+25. 0 
55 
0. 30 p. m. 
1971. 1 
1934. 0 
1903. 8 
— 56. 7 
— 20. 2 
+ 10. 6 
58 
1. SO p. m. 
1917. 7 
1906. 5 
1876. 1 
— 43. 0 
— 31. 8 
— 1.4 
61 
2. 30 p. m. 
1986. 2 
1943. 3 
1916. 0 
— 63. 9 
— 21. 0 
+ 6.3 
64 
4. 00 p. m. 
1921. 5 
1895. 1 
1874.8 
— 51. 9 
— 25.5 
— 5. 2 
Oct. 
3 
66 
8. 30 a. m. 
1809. 8 
1811. 8 
1811.8 
+ 7.9 
4- 5.9 
+ 5.9 
68 
9. 00 a m. 
1772.7 
1765. 2 
1744. 2 
— 22. 3 
— 14. 8 
+ 6.0 
74 
10. 45 a. m. 
1692.1 
1703. 9 
1675.3 
+ 13.6 
— 25.4 
+ 3.2 
Sept. 
29 
Camp. 
6. 00 p. m. 
1752. 1 
1716. 4 
1752. 3 
+ 11.9 
+ 47.6 
+ 11.4 
Sept. 
30 
Camp. 
6. 00 a. m. 
1746. 6 
1727. 7 
1793. 7 
4- 17.4 
4- 36.3 
—29. 7 
Oct. 
1 
Camp. 
6. 00 a. m. 
1716. 1 
1690. 1 
1757. 1 
4- 47. 9 
4- 73.9 
+ 6.9 
Oct. 
4 
Camp. 
6. 00 p. m. 
1719. 3 
1700. 0 
1738. 8 
+ 44.7 
-f 64.0 
+25. 2 
Oct. 
5 
Camp. 
6. 00 a. m. 
1691. 7 
1649.1 
1749.7 
+ 72.3 
+ 114.9 
+ 14. 3 
Oct. 
2 
Camp. 
6. 00 a. m. 
1630. 4 
1653. 3 
1771. 0 
4-142. 0 
+ 119. 1 
+ 1.4 
Camp. 
6. 00 p. m. 
1768. 1 
1755. 7 
1768. 8 
4- 4.3 
+ 16.7 
+ 3.6 
Oct. 
3 
Camp. 
6. 00 a. m. 
1707.7 
1679.4 
1784. 5 
+ 64.7 
+ 93. 0 
-12.1 
Camp. 
11. 30 a. m. 
1794. 0 
1784. 7 
1760. 2 
— 21.3 
— 12. 3 
+ 12. 2 
Camp. 
12.00 m. 
1780. 2 
1778.2 
1752.4 
— 7.8 
— 5.8 
+20. 2 
Camp. 
3. 00 p. m. 
1797. 0 
1776. 2 
1754. 4 
24. 6 
— 3.8 
+ 18. 0 
Camp. 
6. 20 p. m. 
1740. 2 
1707. 8 
1766. 6 
4- 32.2 
+ 64. 6 
+ 5.8 
Oct. 
4 
Camp. 
6. 00 a. m. 
1714. 6 
1670. 7 
1775.3 
4- 57.8 
+ 101. 7 
— 2. 9 
No trial was made of Mr. Blodget’s empirical table, for, as it was deduced from these very 
observations, they would not give a fair idea of its value. As has been already mentioned, the 
method was tested of using successively each place of observation for the lower station, with 
the next above it for the corresponding upper ; but, as might be expected, errors were found to 
be propagated, and to be very considerably greater than when the sea level was constantly used 
for the lower station. 
The result of this investigation, confirming so fully the accuracy of the new method of com¬ 
putation, cannot but be satisfactory. When it is remembered that two nice adjustments are 
required in reading the barometer, it must be considered that a mean error of 9 feet, amounting 
to only about nine thousandths of an inch of the mercurial column, is a wonderfully close 
approximation, when the difference of the altitudes computed amounts to nearly 3,000 feet. That 
this method has slight causes of inaccuracy, even in theory, is not denied ; but this result tends 
strongly to show that practically their effect is unimportant. It is not supposed that the mean 
error in the altitudes on our survey is so small as 9 feet ; but that the profile is sufficiently 
correct for all the purposes of a preliminary reconnaissance, I have not the slightest doubt. 
