(1) Outline of Investigation.—During the last half-century the temperature of the air has been recorded by thermographs at a number of places, and the registered graphs have been measured and mean daily temperature curves have been calculated from them for each month of the year. The amount of labour entailed in these operations is enormous, and it may well be asked whether the figures cannot be put to some further use. It appears to me that a comparison of the daily curves obtained at various places would furnish important information in regard to climate. To effect this the curves may be represented by Fourier's Series, and the values of the constants at the various places may be compared. Another method of comparison, however, seems to me more promising.