Variation of Temperature in the British Isles, &c. 79 



than the anticyclonic days. Thus there is no prominent effect at 

 Vienna analogous to our second-order effect, but, as in these islands, 

 whatever periodic meteorological temperature effects do exist, appear 

 to be entirely independent of the relative frequency and mean tem- 

 perature of cyclonic and anticyclonic weather. An analysis of the 

 temperature curve for Agra, a typical Continental station in India, has 

 also been made (Table I, Agra). Here there is a conspicuous second- 

 order curve, but its position is entirely different from that of the corre- 

 sponding curve for the British Islands, and its effect is to prolong the 

 summer, whilst the second-order effect which has been discussed above 

 shortens it. The two effects are thus in no way analogous, and this 

 result, combined with the result of the Vienna investigation, makes it 

 seem probable that the ocean plays a paramount part in the causation 

 of the second-order temperature effect which we experience in these 

 islands. 



Analysis of Sea Temperatures. 



With the object of further investigating this point, curves whose co- 

 ordinates arc respectively proportional to the fraction of the year, and 

 to the mean temperature of the sea, based on three years' observations 

 at Shetland, Scilly, and Yarmouth, have been analysed (Table II). 

 The maxima and minima of these curves are all a little later in the 

 year than those of the air-temperature curves, but the lag is approxi- 

 mately the same in all of them, and it is an obvious and striking fact 

 that there is in the periodic variation of marine temperature an effect 

 similar to the second-order effect observed in the periodic variations of 

 atmospheric temperature. Whether this variation of the temperature 

 of the water which surrounds these islands is the cause of the atmo- 

 spheric second-order variation, or whether it is only another effect of 

 the same fundamental cause, does not appear ; but in view of the fact 

 that the marked second-order effect is not seen at Continental stations, 

 it would seem not unlikely that the ocean temperature is the imme- 

 diate cause of our second order periodic temperature variation. 



Analysis of Barometric Differences between London and Valencia and 

 London and Aberdeen. 



Table III gives the results of the analysis of the curves of thirty- 

 year-mean difference of barometric pressure between London and 

 Valencia, and London and Aberdeen, respectively. In each of these 

 curves we again find the prominent second-order effect, although in 

 the curve for London Valencia it is somewhat earlier in its posi- 

 tion than the temperature effect. Thus the magnitude of the baro- 

 metric gradients for southerly and easterly winds shows a similar 

 second order periodic variation to that which has been observed in 

 the atmospheric temperature of these islands. In view of the close 



