94 INDUCTION. 



nature of this cause can only be matter of conjecture, 

 yet if it be, as is not unlikely (and as Laplace's 

 theory suggests,) one and the same individual impulse 

 given to all the bodies at once, that cause, acting at 

 the extreme points of the space occupied by the sun 

 and planets, must, unless defeated by some counteract- 

 ing cause, have acted at every intermediate point, and 

 probably somewhat beyond; and therefore acted, in 

 all probability, upon the supposed newly-discovered 

 planet. 



When, therefore, effects which are always found 

 conjoined, can be traced with any probability to an 

 identical (and not merely a similar) origin, we may 

 with great probability extend the empirical law of 

 their conjunction to all places within the extreme 

 local boundaries within which the fact has been 

 observed ; subject to the possibility of counteracting 

 causes in some portion of the field. Still more con- 

 fidently may we do so when the law is not merely em- 

 pirical; when the phenomena which we find conjoined 

 are effects of ascertained causes, from the laws of 

 which the conjunction of their effects is deducible. 

 In that case, we may both extend the derivative uni- 

 formity over a larger space, and with less deduction 

 for the chance of counteracting causes. The first, 

 because instead of the local boundaries of our obser- 

 vation of the fact itself, we may include the extreme 

 boundaries of the ascertained influence of its causes. 

 Thus the succession of day and night, we know, holds 

 true of all the bodies of the solar system except the 

 sun himself; but we know this only because we are 

 acquainted with the causes: if we were not, we could 

 not extend the proposition beyond the orbits of the 

 earth and moon, at both extremities of which we 

 have the evidence of observation for its truth. With 



