Variation of Temperature in the British Isles, <Cr. 69 



The Effect of Wind-direction on Atmospheric Temperature during tlic Fire 



Years 1876-1880. 



A second classification was then made in which, while the types of 

 weather were still distinguished, curves of the difference between first 

 order curve values and mean daily temperature observed during the 

 prevalence of barometric gradients for each of eight points of the 

 compass, were separately drawn. Each of these curves showed certain 

 characteristics which corresponded with some of those of the second- 

 order curve ; either the February maximum or the May minimum or 

 some other characteristics were prominent, but no single one of the 

 curves for the separate gradients showed a complete curve with all the 

 characteristics of the second-order curve. It was, however, very 

 remarkable that the curves for the same winds during different types 

 of weather were closely parallel a result which confirmed the pre- 

 vious observation that neither the mean difference in temperature 

 between cyclonic and anticyclonic days, nor the relative frequency of 

 their occurrence, could give rise to the second-order variation in 

 atmospheric temperature, or indeed to any other simple periodic effect. 

 It was therefore decided to abandon the separate classification of 

 cyclonic and anticyclonic days. 



Examination of the curves above described showed that the number 

 of days on which any particular wind occurred during a ten-day 

 interval in five successive years, was not sufficient to eliminate the 

 effect of exceptional days from the mean value obtained. A further 

 period, from 1880-1884, was therefore examined, and the curves 

 were constructed from monthly means, instead of from ten-day 

 means, for the nine years. Thus sufficient observations were obtained 

 to give mean values which might be regarded as independent of 

 single exceptional variations from the mean. The observations which 

 were retained for the investigation were those relating to the days 

 which had been previously classed as cyclonic or anticyclonic ; the 

 days which were not classified, on account of the want of any definite 

 indication, were omitted. That this omission did not appreciably 

 affect the results arrived at, may be inferred from the fact that one 

 of the curves (Diagram 6, fig. 1, p. 75) could be obtained in two ways 

 first, by taking the temperature difference and frequency of wind for 

 the included days, and, secondly, by taking the temperature difference 

 from the actual means for all days. The results were quite identical 

 in the two cases. 



Effect of Wind-direction on Atmospheric, Temperature during the Nine 

 Years 1876-1884. 



The effect of wind- direction on temperature was investigated by 

 means of curves whose co-ordinates are respectively proportional to 



