424 ACTUAL WORKING IN ORIGINAL RESEARCH. 



sical and chemical series and tables of constants, is in this 

 case of great assistance, by enabling us to compare the 

 phenomena in groups instead of instance by instance. 

 Every force has its own set of laws, and the presence of 

 each force may be inferred from those laws, and vice versa. 

 As the number of essentially different forms of energy 

 which produce all the varied phenomena on this globe 

 is a very small one, their characters definite, and their 

 modes of operation in nearly all cases also well-defined, we 

 can generally soon determine to which of the forces the new 

 phenomena are not essentially related, and at once dismiss 

 them from our consideration. For example, if the pheno- 

 mena take place in inanimate substances, we can at once 

 dismiss from consideration the vital and nervous powers, 

 and all their modes of action and relations. The pheno- 

 mena of chemistry also are usually of so distinct a kind, 

 taking place according to the law of definite proportion 

 by weight, that we can in most cases soon decide whether 

 chemical force is involved in the case or not ; if there is 

 no permanent change of property or alteration of weight 

 of the substances, chemical action has not occurred. 

 Following up this process of exclusion, we usually soon 

 find one or at most two forces to which only the phenomena 

 can be related or due. By now remembering the various 

 chief ways in which those forces act, and the kind or class 

 of substances in which each of them is manifested, we are 

 often enabled to judge which is likely to be the cause. 

 For instance, if the substance employed contains iron, and 

 is attracted or moved by a magnet, we consider it pro- 

 bable that the attraction is magnetic ; but if the substance 

 is non-metallic, and is first attracted into contact with 

 and then repelled by an electrified body, we conclude that 

 the attraction is electric ; and if the phenomenon is 

 electric, we can usually tell whether it is static or dynamic, 



