70 Messrs. "W. N. Shaw and II. "W. Cohen. On the Seasonal 



the period of the year and to the difference on any day hetween the 

 observed mean daily temperature for the nine years and the tempera- 

 ture which would be represented on that day by the first order sine 

 curve obtained by analysis of the twenty-five-year curve. The eight 

 curves so obtained will be spoken of as the temperature curves for 

 each wind; but it must be remembered that they do not represent 

 observed temperatures, but differences between mean observed tem- 

 peratures and temperatures given by the first-order curve at any 

 given period of the year. 



The term " for each wind " also requires some amplification. 

 Owing to the marked effect of local geographical conditions at any 

 station, the recorded direction of the wind does not necessarily give a 

 very accurate estimate of the true quarter from which the station was 

 obtaining its air supply, and it is of course the source of air supply 

 which will affect the atmospheric temperature at any station. The 

 days were, therefore, not classified according to the direction of the 

 wind recorded as having been observed at Kew, but according to the 

 direction of the gradient (high to low) at right angles to the isobars 

 in the neighbourhood of the station, and a curve has been called the 

 curve for the east wind when it really represents a curve for a southern 

 gradient, and so on for other directions. It must be observed that 

 the term " east " is not quite accurate, since the direction of air 

 supply for a southern gradient will not be from due east, but from a 

 little north of east. However, as we are only dealing with eight 

 points of the compass, the direction of the wind when the gradient is 

 to the south will be described with sufficient accuracy as an east wind. 



In Diagram 3 the temperature curves for each wind are given. It will 

 be seen that each curve tends to resemble in some important respects, 

 and in kind, if not in degree, the second-order curve for the twenty-five- 

 year means. For example, the east wind temperature curve has a 

 minimum in the beginning of May, and maxima in August and 

 February ; but these are not equal minima and maxima, and the curve 

 is obviously not simply harmonic. The north-east wind has a mini- 

 mum in spring and autumn and a maximum in winter and summer, 

 although the dates do not exactly correspond with those of the east 

 wind. The curve for the north wind is irregular but has a distinct 

 absolute maximum at the end of July. The curve for the north-west 

 wind has its maxima in February and at the end of July, and minima 

 in spring and autumn, and so on. Thus all the winds have curves 

 whose characteristics suggest those of the second-order curve, although 

 they are not identical with them, and the effect represented by the 

 second-order curve is still apparent in the temperature curves for each 

 separate direction of air supply, and consequently is to some extent 

 independent of the quarter from which the air is supplied. 



