-1859] WRITINGS OF JOSEPH HENRY. 213 



which unavoidably arise among different investigators, have 

 not always been carried on with the calmness and modera- 

 tion with which the pursuit of truth should always be con- 

 ducted. Indeed, meteorology has ever been a source of con- 

 tention, as if the violent commotions of the atmosphere 

 induced a sympathetic effect in the minds of those who have 

 attempted to study them. 



We have stated in the previous articles that we have no 

 h3^potheses of our own to advocate ; and while we attempt 

 to reduce the multiplicity of facts which have been collected 

 in regard to this subject to general principles, we shall aim 

 at nothing but truth, and endeavor to select from the various 

 hypotheses which have been proposed, such as in our judg- 

 ment are well founded on the established laws of force and 

 motion, and which give the most faithful and explicit ex- 

 pression of the phenomena. "We shall be ready at any time 

 to modify or change our views as soon as facts are discovered 

 with which they are incompatible, and indeed we shall hold 

 most of them as provisional truths which may serve to guide 

 our inquiries and which are to be established, modified, or 

 rejected by the results of subsequent induction. While the 

 general principles of meteorology are well understood, the 

 facts relating to it on account of the variations and multi- 

 plicity of condition are the most complex of those of any 

 branch of physical science. It has been properly said that 

 astronomy is the most perfect of all'branches of knowledge 

 because its elements are the most simple; and we may say, 

 for a like reason, that meteorology is the least advanced be- 

 cause its phenomena depend upon the concurrence of so 

 many and so varied causes. 



Vapor of the Atmosphere. 



The air at all times contains water in an elastic, invisible 

 state, called vapor. To prove this it is sufficient to pour a 

 quantitv of cold water into a bright metallic or glass tumbler, 

 the outside of which will become covered with dew. If the 

 vessel were pervious to the liquid we might suppose the water 

 which appears on the outside to come from within, but this 



