Page:Weather Facts and Predictions.djvu/16

 about twenty-seven inches (27.00), which has happened, though rarely (even in the tropics).

In general, the three causes act much less strongly, and much less in accord; so that ordinary varieties of weather occur much more frequently than extreme changes.

The height of the barometer varies according to the elevation of the place of observation above the level of the sea. Meteorologists having agreed to refer all their barometrical observations to the sea-level as the standard level, it is necessary to add to each barometer reading a certain correction (one-tenth of an inch) for every hundred feet that the barometer read is so elevated above the sea, otherwise barometer readings at different stations would not be mutually comparable.

The Thermometer and Temperature.

In the northern hemisphere the daily range of the temperature is least in winter, augments largely in March and April, reaches a maximum in May or June, continues high during the summer, and diminishes rapidly in October and November to the minimum in winter.

A small daily range, coupled with a high dew point, is thought to be indicative of rain.

The daily range is least in wet climates, and in the tropics and Polar regions, and is greatest in dry climates, and in countries in the temperate zones. [Hence it is less in Ireland than in Scotland; greater in England than in either of these countries, and is greater still on the continent of Europe.]