-1859] WRITINGS OF JOSEPH HENRY. 45 



a successful mathematical analysis. In the investigation of 

 a phenomenon, it is not enough that we explain how it is 

 produced ; besides this, positive science requires that the ex- 

 planation be true in measure as well as in mode, and indeed 

 it is only when we can predict the exact amount of an effect, 

 the principle being known and certain data given, that a 

 phenomenon can be said to be perfectly analyzed. We have 

 seen in the preceding paragraphs that the meteorological 

 phenomena produced by astronomical causes admit of rela- 

 tive numerical expression ; but in what follows we are obliged 

 to content ourselves with the explanation in mode, and to 

 refer to direct experiment and observation for the amount 

 of the effect in measure. It is in this part of meteorology 

 that so much uncertainty prevails, and in reference to which 

 so much discussion, even of an excited character, has arisen. 

 As was said before, the writer has no hypothesis of his own 

 to advance and will therefore confine himself to a statement, 

 and in some cases a brief examination, of such hypotheses 

 relative to the effects of the atmosphere, the ocean, &c., in 

 modifying climate as have been suggested, and which appear 

 to be in accordance with established principles. 



Effects of the Atmosphere in a Statical Condition. — Were it 

 not for the aerial envelope which surrounds our earth, all 

 parts of its surface would probably become as cold at night, 

 by radiation into space, as the polar regions are during 

 the six months' absence of the sun. The mode in which 

 the atmosphere retains the heat and increases the tem- 

 perature of the earth's surface may be illustrated by an 

 experiment originally made by Saussure. This physicist 

 lined a cubical wooden box with blackened cork, and, 

 after placing within it a thermometer, closely covered it with 

 a top of two panes of glass, separated from each other by 

 a thin stratum of air. When this box was exposed to the 

 perpendicular rays of the sun, the thermometer indicated a 

 temperature within the box above that of boiling water. 

 The same experiment was repeated at the Cape of Good 

 Hope, by Sir John Herschel, with a similar result, which was 

 however rendered more impressive by employing the heat 

 thus accumulated in cooking the viands of a festive dinner. 



