Page:Proceedings of the Royal Society of London Vol 69.djvu/90

82 metrical process. Thus, if the length of AB, in fig. i, represents the amplitude of the resultant curve, AC, CB, the amplitudes of the two components, then, upon forming a triangle of the three, as in the figure, the angle BCC will represent the phase difference of the two components, BAG will represent the phase difference between the resultant and the first component, and ABC the phase difference between the resultant and second component.

Applying these to the case under consideration, AC may be re- garded as representing the temperature oscillation undisturbed by the effect of the sea temperature, CB the effect of the sea and AB the result- ant effect or the actual temperature oscillation observed at the station. The angle ABC will represent the number of degrees of phase differ- ence between the sea curve and the station curve, i.e., practically, the number of days between the time of maximum on shore and on sea, and so on for the other angles. Of such a triangle for any station, the following elements are known : the resultant amplitude AB, the lag of the sea effect behind the land curve, i.e., the angle ABC. The position of C is indeterminate because we do not know the actual magnitude of the sea effect BC, nor the magnitude or epoch of the undisturbed effect. But we know the extreme position of AC : it cannot correspond to a curve with an earlier maximum than June 21,