•260 INDUCTION. 



experimental inquiry. Considering the whole assemblage of con- 

 cun-ent causes which produced the phenomenon, as one single cause, 

 it attempts to ascertain that cause in the ordinary manner, by a com- 

 parison of instances. This second method subdivides itself into two 

 different varieties. If it merely collates instances of the effect, it is a 

 method of pure observation. If it operates upon the causes, and tries 

 different combinations of them in hopes of ultimately hitting the 

 precise combination which will produce the given total effect, it is a 

 noiethod of experiment. 



In order more completely to clear up the nature of each of these 

 three methods, and determine which of them deserves the preference, 

 it will be expedient (conformably to a favorite maxim of Lord Chan- 

 cellor Eldon, to which, though it has often incurred philosophical 

 ridicule, a deeper philosophy will not refuse its sanction), to "clothe 

 them in circumstances." We shall select for this purpose a case 

 which a,s yet furnishes no very brilliant example of the success of any 

 of the three methods, but which is all the more suited to illustrate the 

 difficulties inherent in them. Let the subject of inquiry be, the condi- 

 tions of health and disease in the human body ; or (for greater simpli- 

 city), the conditions of recovery fi-om a given disease ; and in order 

 to nan-ow the question still more, let it be limited, in the first instance, 

 to this one inquiry: Is, or is not some particular medicament (mer- 

 cury, for instance), a remedy for that disease. 



Now, the deductive method would set out from known properties 

 of mercury, and known laws of the human body, and by reasoning 

 from these, would attempt to discover whether mercury will act upon 

 the body when in the morbid condition supposed, in such a manner as 

 to restore health. The experimental method would simply administer 

 mercury in as many cases as possible, noting the age,, sex, tempera- 

 ment, and other peculiarities of bodily constitution, the particular form 

 or variety of the disease, the particular stage of its progi'css, &c., re- 

 marking in which of these cases it produced a salutary effect, and with 

 what circumstances it was on those occasions combined. The method 

 of simple observation would compare instances of recovery, to find 

 whether they agreed in having been preceded by the administration of 

 mercury; or would compare instances of recovery with instances of 

 failure, to find cases which, agreeing in all other respects, differed only 

 in the fact that mercury had been administered, or that it h^d hot. 



§ 7. That the last of these three modes of investigation is applicable 

 to the case, no one has ever seriously contended. No conclusions of' 

 value, on a subject of such intricacy, ever were obtained in that way. 

 The utmost that could result would be a vague general impression for 

 or against the efficacy of mercury, of no real avail for guidance unless 

 confirmed by one of the other two methods. Not that the results, 

 which this method strives to obtain, would not be of the utmost possi- 

 ble value if they could be obtained. If all the cases of recovery which 

 presented themselves, in an examination extending to a great number 

 of instances, were cases in which mercury had been administered, we 

 might generalize with confidence from this experience, and should 

 have obtained a conclusion of real value. But no such basis for gene- 

 ralization can we, in a case of this desci'iption, hope to obtain. The 

 reason is that which we have so often spoken of as constituting the 



