132 DISCOURSE ON THE STUDY 



refinement in their performance, as well as a great 

 multiplication in their number, becomes necessary 

 to give them importance. In astronomy, for in- 

 stance, the superior departments of theory are com- 

 pletely disjoined from the routine of practical ob- 

 servation. 



(127.) To make a perfect observer, however, either 

 in astronomy or in any other department of science, 

 an extensive acquaintance is requisite, not only 

 with the particular science to which his observations 

 relate, but with every branch of knowledge which 

 may enable him to appretiate and neutralize the 

 effect of extraneous disturbing causes. Thus fur- 

 nished, he will be prepared to seize on any of those 

 minute indications, which (such is the subtlety of 

 nature) often connect phenomena which seem quite 

 remote from each other. He will have his eyes as 

 it were opened, that they may be struck at once with 

 any occurrence which, according to received theories, 

 ought not to happen ; for these are the facts which 

 serve as clews to new discoveries. The deviation 

 of the magnetic needle, by the influence of an 

 electrified wire, must have happened a thousand- 

 times to a perceptible amount, under the eyes of 

 persons engaged in galvanic experiments, with philo- 

 sophical apparatus of all kinds standing around them ; 

 but it required the eye of a philosopher such as 

 Oersted to seize the indication, refer it to its origin, 

 and thereby connect two great branches of science. 

 The grand discovery of Malus of the polarization 

 of light by reflection originated in his casual remark 

 of the disappearance of one of the images of a 

 window in the Luxembourg palace, one evening, 



