the judgment of a careful observer may be more trustworthy than an imperfectly adjusted instrument. At times, too, there may be momentary periods of sunshine which are not registered at all. Even in the absence of all measuring instruments, an observer whose record consists merely of the total of overcast days is gathering information of great value.
Concrete Results of Sunshine Records.—It is well to bear in mind that the mere gathering and tabulating of monthly statistics of sunshine is not an end, but merely a means to an end. Knowledge of any sort possesses but little value unless it can be applied to the betterment of humanity. In agriculture the results may be applied so as to obtain more definite knowledge concerning the growth and maturity of plants—essentially the minimum amount of sunshine necessary to fructification. In almost every department of agriculture the total of sunshine has a direct bearing on the amount of evaporation.
In climatology, much more information concerning the relation of sunshine to public health is required. The healing value of sunlight is not overestimated; its value in therapy of the mind is underestimated. The mental depression following prolonged spells of overcast skies is marked.
In commerce and transportation, the effects of obscuration on visibility is becoming a matter of systematic study and investigation. The impairment of visibility costs more than money; its toll of human life is heavy.
In military and naval strategy, helio-signaling depends on sunshine; so also, sunshine is the key to many problems involving visibility.
The efforts of a single observer may not solve general problems, but they will go a long way in solving the specific cases of his own bailiwick. The observer may determine whether or not specific times of obscuration—daily or seasonal—prevail. In many parts of the country good beginnings have been made already by volunteer observers. Incidentally, there is no station, permanent or transient, from which additional information would not prove of value.
The area in which the per cent of sunshine is less than 40 is very small, and but little of it is crop-growing land. The region of greatest sunshine, for the greater part, is deficient in rainfall. Irrigated lands, however, produce crops that are
