EXAMPLES OF THE FOUR METHODS. 305 



Joint Method. For, as we have ah'eady seen, the defect of that Method is, 

 that like the Method of Agreement, of which it is only an improved form, 

 it can not prove causation. But in the present case (as in one of the steps 

 in the argument which led up to it) causation is already proved; since 

 there could never be any doubt that the rigidity altogethei', and the putre- 

 faction which follows it, are caused by the fact of death : the observations 

 and experiments on which this rests are too familiar to need analysis, and 

 fall under the Method of Difference. It being, therefore, beyond doubt 

 that the aggregate antecedent, the death, is the actual cause of the whole 

 train of consequents, whatever of the circumstances attending the death 

 can be shown to be followed in all its variations by variations in the effect 

 under investigation, must be the particular feature of the fact of death on 

 which that effect depends. The degree of muscular irritability at the 

 time of death fulfills this condition. The only point that could be brought 

 into question, would be whether the effect depended on the irritability it- 

 self, or on something which always accompanied the irritability : and this 

 doubt is set at rest by establishing, as the instances do, that by whatever 

 cause the high or low irritability is produced, the effect equally follows ; 

 and can not, therefore, depend upon the causes of irritability, nor upon the 

 other effects of those causes, which are as various as the causes them- 

 selves, but upon the irritability, solely. 



§ 6. The last two examples will have conveyed to any one by whom 

 they have been duly followed, so clear a conception of the use and practi- 

 cal management of three of the four methods of experimental inquiry, as 

 to supersede the necessity of any further exemplification of them. The 

 remaining method, that of Residues, not having found a place in any of 

 the preceding investigations, I shall quote from Sir John Herschel some 

 examples of that method, with the remarks by which they are introduced. 



"It is by this process, in fact, that science, in its present advanced state, 

 is chiefly promoted. Most of the phenomena which Nature presents are 

 very complicated ; and when the effects of all known causes are estimated 

 with exactness, and subducted, the residual facts are constantly appearing 

 in the form of phenomena altogether new, and leading to the most impor- 

 tant conclusions. 



"For example: the return of the comet predicted by Professor Encke a 

 great many times in succession, and the general good agreement of its cal- 

 culated with its observed place during any one of its periods of visibility, 

 would lead us to say that its gravitation toward the sun and planets is the 

 sole and suflicient cause of all the phenomena of its orbitual motion ; but 

 when the effect of this cause is strictly calculated and subducted from the 

 observed motion, there is found to remain behind a residual phenomenon, 

 which would never have been otherwise ascertained to exist, which is a 

 small anticipation of the time of its re-appearance, or a diminution of its 

 periodic time, which can not be accounted for by gravity, and whose cause 

 is therefore to be inquired into. Such an anticipation would be caused by 

 the resistance of a medium disseminated through the celestial regions; 

 and as there are other good reasons for believing this to be a vera causa'''' 

 (an actually existing antecedent), " it has therefore been ascribed to such a 

 resistance.* 



" M. Arago, having suspended a magnetic needle by a silk thread, and set 



* In his subsequent work, Outlines of Astronomy (§ 570), Sir John Herschel suggests an- 

 other possible explanation of the acceleration of the revolution of a comet. 



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