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Mean daily temperature...
Amount of rain and melted snow in inches...
Depth of snow in inches...
Barometer reduced to 32° Fah...
Pressure of vapor in inches...
Percentage of Humidity....

100

BAROMETER.

Barometer reduced to Freezing Point.-In this space are placed the figures which indicate the observations on the barometer reduced to the temp. of 32° Fahrenheit, by means of a table; and also the mean or average of the three reduced daily observations.

FORCE OF PRESSURE OF VAPOR.

In this space are entered the numbers which indicate the inches of mercury of a barometer which the force of vapor of the atmosphere alone will sustain. The whole pressure of the atmosphere, as given under the head of "Barometer," is due, conjointly, to the weight of the air and the moisture which it contains. The figures under this table indicate the separate pressure of the moisture, and are obtained from the records of the wet and dry bulb thermometers by means of a table based on experiment.

RELATIVE HUMIDITY OR PERCENTAGE OF SATURATION.

The quantity of water in a state of vapor which a given space can contain, depends on the temperature. When a given space has as much water as it can hold at a given temperature, it is said to be saturated with vapor. If the temperature be lowered, a portion of the vapor will be condensed into water, but the space will still be saturated. If the temperature be raised and no more vapor be admitted, the space will only be partially saturated. The numbers under the head of "Relative humidity" therefore denote the percentage of saturation; full saturation being indicated by 100, and half saturation by 50. These figures are deduced from the corresponding forces of vapor by means of a table in the Smithsonian Collection.

RESULTS FOR 1878.

44°.54 31.745

652

28.874 .285

82.

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