Se ee Se aee eee ae, Re ee 
E. Loomis—Reduction of Barometric Observations. 93 
The reduced pressures computed from this formula are 
shown in column twelfth of table III, and the differences 
€ 
Sacramento, I have applied to the half sum of the temperatures 
at the upper and lower stations, the corrections shown on page 
20. In the four other cases I have applied no such correction 
because this correction appears to be quite small, and its pre- 
cise value is not very well determined. We see that with low 
pressures the computed reduction to the lower station is (with 
one trifling exception) always too small; but with high press- 
_ ures the computed reduction is (with two trifling exceptions) 
always too great. It has been shown that only a small part of 
these differences can be ascribed to the error in the assumption 
that the mean temperature of the atr column is equal to the 
The discrepancies are mainly due to the dissimilarity in the 
curves representing the barometric fluctuations at the two 
stations, 
In consequence of this dissimilarity, it happens that when 
the barometer on the top of a mountain is at a minimum, the 
barometer at its base is generally not exactly at its minimum, 
or it is a minimum of an inferior order. The barometer at the 
correspondence between the barometric movements at the two 
stations, and the observed difference between the upper and 
lower barometers is greater than that which theory would 
indicate. On the contrary, when the barometer on the top of 
the mountain is at a maximum, the barometer at the base is 
generally not exactly at its maximum, or it is a maximum o 
an inferior order. The barometer at the base is therefore 
lower than it would be if there was an exact correspondence 
between the barometric movements at the two stations, and the 
observed difference between the two barometers is less than 
that which theory would indicate. 
Hence we see the utter hopelessness of discovering a formula 
which shall exactly represent the barometric reduction to sea- 
h 
) ; and since these movements are 
greatly modified by the obstruction of the mountains upon 
half sum of the temperatures at the upper and lower stations. | 
base is therefore higher than it would be if there was an exact . 
level at all pressures and temperatures, unless the formula takes _ 
