148 HABIT AND INTELLIGENCE. [chap. 



sciences are true independently of those of chemistry, and 

 can be understood without them. And the laws of che- 

 mistry are true, independently of those of life, and can be 

 understood without them.^ Thus the series resembles a 

 building of several stories, each of which rests on that 

 below it. 

 Depnnd- Although, in order to avoid circumlocution, I have 

 ^°?^ ^f th* spoken of the sciences as depending the one on the other, 

 sciences, yet iu reality the dependence is not only of the sciences, 

 things. that is to say of our knowledge of the laws, but of the 

 laws of the things themselves. Not only our knowledge 

 of biological laws, but the biological laws themselves, 

 depend on chemical laws. Not only our knowledge of 

 the chemical laws, but the chemical laws themselves, 

 depend on the laws of heat and electricity. The laws of 

 heat and electricity are but cases of the laws of general 

 dynamics. And not only our knowledge of the laws of 

 dynamics, but the laws of dynamics themselves, depend 

 on the laws of mathematics, which are but the statement 

 of the properties of space and time. I am not here in- 

 sisting, as may perhaps be thought, on a merely identical, 

 or self-evident, proposition. It is quite easy to conceive 

 such a relation between two sciences, that our knowledge 

 of the one shall be dependent on our proficiency in the 

 other, without the subject-matters of the two having any 

 Accidental connexion whatever. Such a relation does exist between 

 of his^to™ optics, or the science of light, and histology, or the science 

 logy with of the minute structure of organic tissues. Histology has 

 been created as a science by the microscope, which owes 



^ It may be objected, that this is wrong in point of fact : it may be said 

 that chemical laws are implied in the theory of electric curi'ents, and 

 biological laws in organic chemistry. I reply, that electro-chemistry does 

 no doubt imply chemical laws, and may be regarded as a branch of 

 chemistry, but the whole theory of electro-statics and electro-dynamics may 

 be stated without any chemical knowledge being needed. And as to 

 organic compounds, chemistry works with them just as if they were 

 mineral substances. 



Of course the various sciences run into each other, and have many and 

 varied mutual relations. But I think they are more distinct, and stand in 

 simpler relations to each other, than we might have anticipated. 



