280 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



Malta for replanting the island with trees, in which he re- 

 marks that the characteristic features of the climate of that 

 island are the cold northerly winds of the winter, and the ex- 

 cessive heat of summer, with a great scarcity of water through- 

 out the whole year. The entire absence of trees on the island 

 was thought to intensify and increase these extremes, and it 

 was believed that by securing an abundant covering of for- 

 ests much could be done for the amelioration of the climate. 

 Mr. Buchan, in reference to the general theory of such amelio- 

 ration, states that while the highest temperature of the air 

 occurs in summer between two and three o'clock P.M., the 

 change in the trees is very slow, the leaves not attaining 

 their maximum temperature until nine o'clock P.M. Thus, 

 while the atmospheric changes are rapid, the temperature 

 varies slowly in the trees, and therefore they serve, like the 

 ocean, as equalizers of the temperature, moderating the heat 

 of the day, and maintaining a higher temperature during the 

 night. 



In continuation of the same subject, Mr. Buchan remarks 

 that, as air is heated by contact with the soil, and as trees 

 shelter the soil from the solar radiation, they must diminish 

 the force of the sun's rays, especially in the lower strata of 

 the atmosphere. The exhalation of moisture by trees pro- 

 duces cold in the air by abstracting the latent heat from it. 

 This lowering of the temperature gives to the air a greater 

 degree of humidity. Again, the leaves of trees exercise an 

 important influence in cooling the atmosphere, as the tree 

 itself, by its radiation of heat, becomes sensibly lower in tem- 

 perature, and thus cools the air as it plays among the leaves. 

 18 A, February 17, 514. 



SUPPOSED NATURAL ORIGIN OF SOME FOREST FIRES. 



The great frequency of fires during summer in the pine for- 

 ests of Germany and France, under circumstances where there 

 was no suspicion of accidental or willful incendiarism, has sug- 

 gested to Mr. Schrader the idea that these may possibly be in 

 a measure spontaneous. In most of these forests the resin is 

 collected in large quantity from punctures made in the bark, 

 and an exudation of the same substance may take place when- 

 ever the bark is accidentally cracked. Mr. Schrader suggests 

 that the tear-shaped drops of resin, in running from the tree, 



