DETERMINATION OF ALTITUDES BY BAROMETER. 
113 
and thus broke the barometer in a way very difficult to repair. It was successfully accomplished, 
however, by putting a little of Husband’s adhesive plaster on both sides of the crack, and 
then covering it with sealing wax dissolve'd in alcohol, to protect it from the dr. 
- INSTRUMENTAL ERRORS. 
In order to eliminate the effect of capillary attraction, of minute bubbles of air which cannot 
be entirely excluded from a tube unprovided with Daniell’s protective ring, and of other causes 
of instrumental error, the scales of all the barometers were so adjusted by the maker that the 
instruments agree'd precisely with Smithsonian standard on leaving New York. On reaching 
Fort Reading, from a mean of over two hundred observations, taken with great care by the 
gentlemen of the party, Nos 1060 and 1061 were found to agree exactly with each other, while 
both Nos. 1068 and 1089 differed slightly from them. It was assumed that the two former had 
remained unchanged ; and corrections to make each of the others agree with them were dedu 'ed 
from the above mentioned observations, after the temperature of the mercury had been reduced 
to 32° Fahrenheit. Subsequently, whenever a barometer was broken and re-filled, a similar 
correction was deduced. The following table exhibits these corrections. 
Barometer No. 1060. 
Date. 
Inches. 
July 10 to September 18_ 
. 000 
+ .022 
+ .023 
+ .042 
+ . 191 
September 19 to September 29__ _ 
September 30 to October 15____ 
October 1(5 to October 29_ 
Subsequent to October 29_ 
Barometer No. 1061. 
B Date. 
Inches. 
July 10 to August 5_ _ _ 
. 000 
Irreparably broken on August 5_ 
• 
Barometer No. 1068. 
Date. 
Inches. 
During wliole surveyl_ 
* — . 009 
Barometer No. 1089. 
Date. 
Inches. 
July 10 to August 5_ 
-f .015 
-f- .044 
+ .035 
August G to September 4_ 
Subsequent to September 4_ 
15 X 
