E. Loomis— Contributions to Meteorology: 15 
formula with constant coéfficients should provide for the im- 
mense variety of conditions which prevail in the neighbor- 
hood of mountain stations; and we may be compelled for each 
mountain region to adopt tables founded upon a direct com- 
parison of observations made at stations of different elevations 
and not very remote from each other. 
I have endeavored to represent by formule of a different 
kind the observed values of the reduction given in the preced- 
ing tables. They may all be rudely represented by expres- 
sions of the form 
Reduction =X—Y d T+Z dB, 
where X represents the value of the reduction for a mean 
temperature and pressure; Y represents the change in the 
reduction caused by an increase of 1° in temperature; and Z 
represents the change caused by an increase of 0°1 inch in the 
barometer; but this formula is not sufficiently accurate to be 
of any use. The formula is improved by adding a term repre- 
senting the variability of the temperature correction. e 
following expression represents very well the observed values 
of the reduction for Mt. Washington. 
Reduction = 
6-499 —0-0164 d T+0:°0039 d B+-0:07 sin (4°°235 dT—41°'175), 
represent these values with differences perhaps no greater than 
their probable errors. For this purpose I take the mean of all 
the observed values corresponding to the temperature —10°, and 
also determine the average correction at that temperature for a 
change of 0-1 inch in the barometer. I do the same for the 
temperature —5°, and so on through the table. By applyin 
the proper barometric correction, these averages are all reduc 
to the barometric height 23°5 inches. 
In the following table, column 1st shows the degrees of the 
thermometer (Fah.) from — 10° to + 80°; column 2d shows for 
each temperature the mean reduction to sea-level when the 
barometer on Mt. Washington stands at 23-5 inches; and col- 
umn 3d shows the correction due to a change of 0-1 inch in the 
