DIFFERENT DEGREES OF SCIENTIFIC CERTAINTY. 143 



principles of conservation of matter and of force, the cor- 

 relation of the physical forces, the law of gravity, &c. 



The degree of certainty we are justified in feeling in a 

 scientific truth depends entirely upon the evidence in 

 support of it, and upon the degree to which we understand 

 it. The extent to which we are able to comprehend a 

 truth of science depends upon the degree of simplicity of 

 the truth itself, and upon our knowledge of the particular 

 subject. Different scientific subjects are not to a finite 

 mind equally easy to understand ; and those which are 

 but little developed, only future generations will be able 

 fully to comprehend. There are some, however, in which, 

 more so than in others, he who seeks the truth may find 

 it. This is especially the case with the simpler experi- 

 mental ones, such as physics and chemistry, and is pro- 

 bably the reason why such immense material advantages, 

 and others far more important to mankind, have already 

 resulted from their investigation. Other sciences, such as 

 the biological and concrete ones, are, in consequence of 

 their greater complexity, more difficult to understand, and 

 require those who investigate them to receive previously 

 a more varied mental training ; they are also to a large 

 extent dependent for their advancement upon the previous 

 development of physics and chemistry. Those subjects 

 which are the most simple in themselves, which have 

 been the most perfectly developed, and which we have 

 most studied, we are usually the best able to understand. 

 Others again, in consequence of the sciences preliminary 

 to them not being sufficiently advanced, do not at pre- 

 sent afford the data necessary to enable us to arrive at a 

 high degree of certainty ; for instance, the art of curing 

 disease is very imperfect, partly owing to this cause ; 

 others, such as the 'historical, mental, and linguistic 

 sciences,' and various of the 'concrete sciences,' from 



