Of the many ways in which a traveller may add to the knowledge of atmospheric conditions, five may be specially mentioned:—
1. A record of the weather, observed day by day with regard both to non-instrumental observations and the readings of instruments. This may be taken as the minimum incumbent on all travellers.
2. Observations for forecasting the weather and obtaining warning of storms. This is sometimes of vital importance; it is always valuable at the time, and occasionally the results are worth recording. It may, however be looked upon as a practical application of the systematic observations.
3. Observations with a view to determining the character of the local climate. The traveller passing through a country can do little in this way, as long continued uniform observations in one place are necessary to fix the annual variations. Still, the recording of such data as may be obtained is always important in a little-known region, and the work of several travellers at different seasons will allow some fair deductions to be drawn. When a day is spent in camp, much importance attaches to regular observations made every two hours, from which the diurnal changes of climate may be ascertained.
4. Special meteorological researches. These usually demand special instruments and skilled observers. Observations in the upper air by kites or balloons in particular, must be an end in themselves. Exact measures of radiation in deserts, of rainfall in forests and on adjacent open ground, of temperature during land and sea breezes, or of fogs, thunderstorms, tornadoes, etc., in places subject to those visitations, are always of value. As a rule, however, the traveller cannot devote much time to these matters, unless the study of physical geography is the object of his journey.
5. The collection of existing meteorological records. It sometimes happens that at outlying stations meteorological observations have been taken and recorded for a considerable time. If they have not been already communicated to some meteorological centre, the traveller should obtain a copy of them, and also compare the instruments in use with his own. He might in some cases aid in securing a knowledge of local climate by inducing residents at outlying stations to start regular observations.
The first two ways of advancing meteorology need alone be considered in detail; but with regard to all, it must be clearly understood that the value of the work is greater the more carefully the observations are made and recorded, and the more remote and less known the region.
1. A Record of Weather.—The traveller who makes his journey for any other purpose than the study of physical geography would be wise to burden himself as little as possible with instruments, but to understand thoroughly and use faithfully the few he carries. In a rapid march many different climates may be traversed in a few weeks, and the records of variation of weather so obtained could not have much value; but when a halt of a few days or of a week or two is made, systematic observations become valuable.