REMARKS ON THE THERMOMETER B. W. USED BY MR. S. W. BAKER IN
DETERMINING HEIGHTS. By Staff-Commander C. George,
Curator of Maps, Royal Geographical Society.
This thermometer was one of the three supplied by the Royal Geographical
Society to Consul Petherick, in 1861, and was made by Mr. Casella.
At Gondokoro, in March, 1862, it was lent to Mr. Baker, who made all his
observations with it, and brought it back safe: it has, therefore, been
in use about 4 and 3/4 years.
On November 9th, 1865, Mr. Baker returned it to the Royal Geographical
Society, and it was immediately taken to Mr. Casella, who tested its
accuracy by trying its boiling-point, in nearly the same manner as Mr.
Baker had made his observations. The result by two independent observers
was that the boiling-point had increased in its reading by 0 degree
point 75 in 4 and 3/4 years, or 0 degree point 172 yearly.
On November 23d the thermometer was again tested by Mr. Baker at the Kew
Observatory. The observation was made under the same conditions as those
near the Albert N'yanza, as nearly as it was possible to make it. (By
immersion in boiling water.) The result gave the thermometer 0 degree
point 80 too much at the boiling-point.
The readings of the thermometer have, therefore, been TOO MUCH; and by
REDUCING the readings, it ELEVATES all positions at which observations
were made.
Table No. 1. - In this Table the error obtained at Kew Observatory has
been treated like that of a chronometer, the error being assumed
increasing and regular.
Table No. 2 is to correct the height, computed by Mr. Dunkin, using the
quantity taken from Table No. 1.
Table No. 3 is the final result of the observations for height,
corrected for instrumental error.
TABLE No. 1.
Table for Increased Reading of Thermometer, using 0 degrees 80 as the
Result of Observations for its Error.
Month. 1861. 1862. 1863. 1864. 1865.
January. . . - 0'143 0'314 0'487 0'659
February . . - '157 '328 '501 '673
March . . . 0'000 '172 '344 '516 '688
April . . . '014 '186 '358 '530 '702
May . . . . '028 '200 '372 '544 '716
June . . . . '043 '214 '387 '559 '730
July . . . . '057 '228 '401 '573 '744
August . . . '071 '243 '415 '587 '758
September . . '086 '257 '430 '602 '772
October . , . '100 '271 '444 '616 '786
November . . '114 '285 '458 '630 0'800
December . . 0'129 0'300 0'473 0'645 -
TABLE No. 2.
At the elevation of 3,500 feet, 1 Degrees equals about 520 feet, from
which the following -
Degrees Feet. Degrees Feet Degrees Feet.
1'0 . . . 520 '7 . . . 364 '3 . . . 156
'9 . . . 468 '6 . . . 312 '25 . . . 130
'8 . . . 416 '5 . . . 260 '2 . . . 104
'75. . . 390 '4 . . . 208 '1 . . . 52
End of The Albert N'Yanza, by Sir Samuel W. Baker
