and embolden enquirers to predict in other like cafes. Though we should not be content with an imperfect argument where a perfect one was attainable, there is a peculiar pleasure in finding that our imperfect one is confirmed by fubfequent obfervations; and this is one of the principal rewards of the natural philosopher for his laborious refearches. We shall be prepared then to find that defective arguments, fuch as are employed in other fubjects, occur in the inductive method also.

$89. Caufes and Laws.

It is difficult to define accurately what we mean by a natural cause, and to distinguish it from a natural law. Gravitation is the cause of the fall of a stone; and the stone falls in obedience to the law of gravitation. But in the notion of cause we feem to imply power and energy; a man causes the death of another, who by his own act and power brings death upon him. In the field of nature power can only be improperly and metaphorically attributed to caufes. All power refides in

the great First Cause, and the earth has not, in the proper fenfe of the word, power to attract the ftone, fo much as a neceffity of attracting it. We may notice that a principle may be regarded as cause or law according as we look on it in connexion with the thing produced, or with the higher neceffity that produces it; in the former case we affign it the notion of power, as being the immediate channel of a power that flows from a higher fountain, and in the latter we attribute to it rather the notion of fubjection and neceffity, and look for the producing power at some higher link in the chain.

In order to constitute any fact or principle, the cause of other facts, it should poffefs the following characters.*

A. "Invariable connexion, and, in particular, invariable antecedence of the cause and confequence of the effect, unless prevented by some counteracting cause.”

B. "Invariable negation of the effect with absence of the cause, unless some other cause

* Sir John Herschel's Preliminary Discourse, p. 151.

be capable of producing the fame effect." The application of this principle has been called the Method of Difference.

C"Increase or diminution of the effect, with the increased or diminished intensity of the cause, in cafes which admit of increase and diminution."

D" Proportionality of the effect to its cause in all cafes of direct unimpeded action."

E "Reverfal of the effect with that of the caufe." The application of the three last principles conftitutes the Method of Concomitant Variations.

From these principles follow fome practical rules for ascertaining causes; fuch as

1. The cause of a given effect may be the fame as we know to produce fome similar effect in another cafe better known to us.

For example, Berzelius records that a small bubble of the gas called feleniuretted hydrogen, infpired by accident through the nose, deprived him for fome hours of the sense of smell, and left a severe catarrh which lafted for fifteen days. Dr. Prout fuggests that

the corresponding effects in Influenza may be traceable to the fame cause as undoubtedly produced them here, to the admixture namely of this or fome similar substance with the air we breathe; and as a fuggeftion or anticipation this is perfectly legitimate, and may prove highly valuable. Its inadequacy as a proof may be shewn by throwing it into fyllogistic form

The case of inspiring seleniuretted hydrogen is a case in which lofs of fmell and fevere catarrh follow;

Cafes of influenza exhibit these effects,

Therefore cafes of influenza are cases in which the faid gas has been inspired.

This is the mood A A A, Fig. ii. invalid because it does not diftribute the middle term (p. 234). It is one of the arguments described as Rhetorical Enthymemes in the last fection.

2. "If in any of the facts we have to account for, there be even one in which a particular character is wanting, that character cannot be the cause in question; for the true caufe can never be absent."

3. As the laws of nature are uniform, and

never capricious, we are entitled to expect that a cause which in feveral cafes produces a given effect will always do fo; and if it appears to be otherwise, we should either search for fome counteracting causes, or suspect the accuracy of our obfervations.

4. "Caufes will very frequently become obvious by a mere arrangement of our facts in the order of intensity in which some peculiar quality fubfifts: though not of neceffity, because counteracting or modifying caufes may be at the fame time in action."

"For example: found confifts in impulfes communicated to our ear by the air. If a series of impulses of equal force be communicated to it at equal intervals of time, at first in flow fucceffion, and by degrees more and more rapidly, we hear at first a rattling noise, then a low murmur, and then a hum, which by degrees acquires the character of a mufical note, rifing higher and higher in acuteness, till its pitch becomes too high for the ear to follow. And from this correfpondence between the pitch of the note and the rapidity of fucceffion of the impulfe, we conclude that