224 Notices respecting New Books. 



cond to none at present living. The name of Captain Sabine 

 is so well known among us, that it is sufficient to mention it, 

 in order to enable our readers to appreciate the great value of 

 his ard and zealous support to our author. His communica- 

 tions form a considerable portion of the volume before us, and 

 have all that clearness of detail, and philosophical precision, 

 for which his papers in the Transactions of the Royal Society 

 of London are so remarkable. 



The Third Essay is upon the subject of the radiation of heat 

 is the atmosphere. We have already devoted so much space 

 to the preceding topics, that we can only state a few of the most 

 important facts that are there detailed. It is shown, conclu- 

 sively, from a comparison of observations, under the equator, 

 in temperate climates, and within the arctic circle, that the 

 excess of the heat derived from the direct rays of the sun, above 

 the temperature of the air, is much greater in high than in low 

 latitudes. This is evidently a most bountiful provision of Pro- 

 vidence, in equalizing the effect of different climates, and fitting 

 them all to be inhabited by the human race. We may in this 

 way account for the facts, that the hottest days in high lati- 

 tudes are nearly as oppressive to the mere senses, as in low 

 latitudes, where the thermometer stands much higher ; and 

 that vegetation is so very rapid in cold countries after the ice 

 and snow are dissipated. Mr. Daniell has given a very inge- 

 nious hypothesis, by which he accounts for this curious phe- 

 nomenon. The air, as we have seen, exerts a pressure on 

 every part of the earth that, taken at a mean, is equal ; in high 

 latitudes, however, the air is the most dense, and the atmo- 

 sphere assumes in consequence the figure of a spheroid very 

 much flattened towards the poles. Our author supposes that 

 the depth of this atmosphere, at each particular place, has an 

 influence on the quantity of heat that is transmitted. 



The heat that is communicated by the sun to the earth again 

 radiates ; the rate of radiation will be affected by a variety of 

 circumstances, such as the presence or absence of the sun, the 

 temperature of the radiating surface, and the state of the hea- 

 vens. Dr. Wells, it may be mentioned, has made a most im- 

 portant use of this subject in explaining the formation of dew. 

 Mr. Daniell finds, that radiation from the earth follows the 

 same law as the direct radiation from the sun, being propor- 

 tionably less in low than it is in high latitudes ; and lie applies 

 the same explanation to this as to the other circumstance. He 

 lastly details an experiment by which he shows, most conclu- 

 sively, not only that the rays of the moon do not communicate 

 any sensible heat, but that its light does not affect the terres- 

 trial radiation, even as much as the slight cloud that hardly ob- 

 scure* 



