xlix 



above tliat of the mainland was clearly shown on the dia- 

 grams, as was the influence of the equable relative coolness 

 of the water in summer in reducing the heat of that season, 

 varying in both cases most sensitively with the direction of the 

 wind. Thus the thermometrical curves for Scilly were exhibited 

 passing high above those for Truro and Greenwich in the winter 

 months, falling far below the latter in summer, and nearly 

 blending with them in sj^ring and autumn. But it was pointed 

 out that this action was still more conspicuous and more impor- 

 tant in its bearing on the extremes of heat and of cold, a matter 

 of much more consequence as regards animal and vegetable life 

 than the average temperature. It was shown by a comparison of 

 all the more remarkable periods of hot and of cold weather 

 during the four years, 1871 to 1874, the wind in both cases 

 having been almost always more or less easterly, that while in 

 all the 24 hottest days taken together, the greatest heat in the 

 islands was 7r25, that at Truro being 77-96, or 6-71 degrees 

 higher, the difference in some instances was twice as great, and 

 in one even 1 5 degrees ; and that while the average difference in 

 the 30 coldest days was 11 • 1 6 degrees, the mean at Truro being 

 27-07 degrees, that at Scilly 38 23, the difference on particular 

 days of very severe cold was much greater, sometimes even 20 

 degrees, having been on Nov. 12th, 1871, 23 degrees at Truro, 

 and 43 degrees at Scilly. 



The following illustrations of high and low temperature from 

 the year 1871 may serve as specimens :- — 



Such is the effect of the temperature of the sea on the air 

 passing over it for thirty miles, and a measure is thus furnished 

 of the influence of the air coming over the land from the same 

 sea. Accurate observations of this sea temperature are now 

 being made at the Seven Stones Lightship, under the direction 

 of the Meteorological OflB.ce, and we are indebted to Mr. Dymond 

 for an excellent record for three years off the coast of Falmouth ; 

 the highest praise is also due to Mr. Whitley, who many years 



