528 INDUCTION. 



being sufficiently powerful without it. Neither, there- 

 fore, will the instances of recovery agree in the admi- 

 nistration of mercury, nor will the instances of failure 

 agree in the non-administration of it. It is much if, 

 by multiplied and accurate returns from hospitals and 

 the like, we can collect that there are rather more 

 recoveries and rather fewer failures when mercury is 

 administered than when it is not ; a result of very 

 secondary value even as a guide to practice, and almost 

 worthless as a contribution to the theory of the subject. 



8. The inapplicability of the method of simple 

 observation to ascertain the conditions of effects de- 

 pendent on many concurring causes, being thus recog- 

 nised ; we shall next inquire whether any greater 

 benefit can be expected from the other branch of the 

 a posteriori method, that which proceeds by directly 

 trying different combinations of causes, either arti- 

 ficially produced or found in nature, and taking notice 

 what is their effect : as, for example, by actually trying 

 the effect of mercury, in as many different circum- 

 stances as possible. This method differs from the one 

 which we have just examined, in turning our attention 

 directly to the causes or agents, instead of turning it to 

 the effect, recovery from the disease. And since, as a 

 general rule, the effects of causes are far more acces- 

 sible to our study than the causes of effects, it is 

 natural to think that this method may be successful 

 although the former must necessarily fail. 



The method now under consideration is called the 

 Empirical Method ; and in order to estimate it fairly, 

 we must suppose it to be completely, not incom- 

 pletely, empirical. We must exclude from it every- 

 thing which partakes of the nature not of an expe- 

 rimental but of a deductive operation. If for instance 



