w= 
a 
2 E. Loomis— Contributions to Meteorology. 
8 
Plantamour, as developed in the Tables of Colonel Williamson 
(Professional Papers of the Corps of Engineers, No. 15). In 
tween this result and the preceding gives the observed reduc- 
tion of the Mt. Washington observations to sea-level. The 
mean of the temperatures at Burlington and Portland was taken 
to represent the temperature at the base of Mt. Washington, 
and the mean between the temperatures at the summit an 
base was regarded as the mean temperature of the column of 
air extending from the summit of the mountain to sea-level. 
When several months of the eight years observations gave about 
the same temperature and pressure, they were combined in a 
single mean. I thus obtained thirty values of the reduction 
from summit to sea-level, for a considerable range of tempera- 
ture and pressure. 
In order to extend the comparison to the greatest possible 
range of temperature and pressure, I selected the following list 
of dates from the published volumes of the tri-daily observa- 
tions, now embracing a period of thirty-six months. 1. All 
the dates on which the thermometer on Mt. Washington fell 
ten degrees below zero, and also all the dates on which the 
thermometer at Burlington or Portland fell to ten degrees above 
zero. 2. All the dates on which the thermometer on Mt. 
Washington rose as high as 55°, and all the dates on which the 
thermometer at Burlington or Portland rose to 80°. 3. All the 
dates on which the barometer on Mt. Washington or at Bur- 
lington or Portland sunk 0°40 inch below its normal height; 
4, All the dates on which the barometer at either of the sta- 
tions rose 0°30 inch above its normal height. These four classes 
together embraced 423 days. For each of these dates, the mean 
pressure on Mt. Washington (from the three daily peinbh seri 
was determined; the mean pressure at Burlington and Port- 
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