i go THE SCIENCE OF LOGIC 



they came from chambers the one four times as large as the other, 

 each chamber being fed by the same stream. A better example 

 is that furnished by the daily, monthly, and yearly variations in 

 the motions of the tides. The cause of those tidal motions, with 

 their periodic variations, had long been unknown, although some 

 connexion of them with the moon had been suspected for centuries. 

 It was only, however, when Newton formulated the law of uni 

 versal gravitation, and when in the light of this law the combined 

 action of the sun and the moon upon the waters of the ocean be 

 gan to be studied, that scientists gradually discovered, in the re 

 lative positions and motions of the sun, moon, and earth, a set of 

 phenomena which varied concomitantly with the variations in the 

 tides, and which, by their variations, accounted satisfactorily for 

 the latter. 



When we have to rely on observation alone, the degree of as 

 surance which the method gives us in any individual inquiry will 

 depend on the likelihood that no other unobserved influences are 

 relevant to the observed variations. In all such cases it may be 

 regarded as a modified application of the method of agreement 

 (single or double). The advantage it has over agreement is this : 

 it enables us to see that the supposed causally connected pheno 

 mena are not merely present in a variety of different instances, 

 but that they vary concomitantly in degree throughout these in 

 stances. This is better than observing merely the presence (or 

 the total absence) of such factors in a number of instances. 



The method is used extensively, by way of observation, in 

 astronomy, in geology, and in the study of climatic phenomena. 1 

 But its use in the biological, social, political, economic, and 

 commercial sciences, is perhaps still more extensive and import 

 ant. 2 The extremely unreliable character of some of the infer 

 ences based upon it, is due to the fact that owing to the impossi 

 bility of sufficient analysis numerous influences really relevant to 

 the varying phenomena remain undetected. Numerous sets of 

 instances exhibiting concomitant variation of the degree of 

 development in &quot; intelligence &quot; with the weight of the brain and 

 other sets exhibiting concomitant variation of the former with the 

 complexity of convolution in the latter have been observed and 



1 Cf. FOWLER, op. cit., pp. 182-87. 



a It is not the employment of this method, but rather the extensive use of the 

 argument from analogy, in certain sciences, that has given currency to the descriptive 

 title &quot; comparative,&quot; in reference to such sciences as e.g. &quot; Comparative Philology,&quot; 

 &quot; Comparative Anatomy,&quot; &quot; Comparative Psychology,&quot; etc. 



