Sciences of Meteorology and Terrestrial Magnetism. 159 



on the earth's atmosphere, the scene in which the phenomena of 

 meteorology are exhibited, in prosecuting those avocations on which life 

 and health depend, man must have given himself to the observation of 

 these phenomena so soon as he began to be " a keeper of sheep," and 

 " a tiller of the ground," and " to eat bread in the sweat of his brow." 

 In the Sacred Scriptures, and in ancient profane writers — as Hesiod's 

 Works amd Days, in Homer and Virgil, we have constant allusion to 

 its real or supposed laws ; and in Hesiod and Virgil many precepts for 

 the guidance of the shepherd, the husbandman, and the mariner. Some 

 such precepts indeed have been for ages established in all nations, and 

 the phenomena connected with an agency emanating from the heavenly 

 bodies ; but most of them have no foundation in any scientific principle 

 or careful induction of facts. Yet are they repeated from day to day 

 by persons of intelligence among ourselves, and pass current as estab- 

 lished laws. The opinion is still too common that meteorology has only 

 for its object to record changes of weather, and enable us to construct 

 weather almanacs ; at least, the numerous registers which have been 

 from time to time published, appear to have no higher aim. It seems 

 never to have struck the observers that such loosely arranged collec- 

 tions of facts, made at stations fortuitously hit upon, would be useless 

 for any purpose of science, or lead to any knowledge of great laws ; 

 while, on the other hand, it requires little scientific enlightenment to 

 imderstand, that exact numerical results, obtained at stations well chosen, 

 and collected for a series of years by means of instruments of a like 

 construction, and carefully compared, would lead, when analyzed, to the 

 discovery of general laws. Such great generalizations are always diffi- 

 cult, as we know from the history of every science, — those especially, 

 like chemistry, physiology, and geology, in which the induction of facts 

 leads to the discovery of laws. In the sciences to which mathematics 

 is strictly applicable it is different. In astronomy, optics, and the 

 various branches of mechanics, we have, in most cases, absolute certainty 

 in the establishment of such laws ; but in other sciences, how often has 

 it happened that the generalizations of one age — or even decade of years 

 — have been upset or largely modified by the more extended induction 

 and wider range of experiment in tlie next age or decade. Now, meteor- 

 ology deals with a subtile element — the gaseous envelope of our globe 

 in its momentarily varying relations to the diffused moisture, to the all- 

 pervading impalpable element of heat, and to that mysterious and 

 powerful agent, the electric fluid. To estimate the mutual action of 

 these, and to eliminate the effects due to each agent, must obviousl}"- 

 require the closest observation, with instruments as perfect as possible, 

 and having a correspondence in their indications of the various elements. 



