206 GENERAL CONDITIONS OF SCIENTIFIC RESEARCH. 



conductors of heat and of electricity, was set aside by 

 the discoveries that ail substances might be arranged 

 in continuous series without a break, from the most 

 perfect conductor to the most complete non-conductor ; 

 and that between positive and negative electric bodies, 

 arid between acids and bases, was removed in a similar 

 manner. That between combustibles and supporters of 

 combustion has also been destroyed. That between 

 organic and inorganic substances was obliterated by the 

 discovery of the synthesis of various organic compounds 

 from inorganic materials ; that between animals and 

 vegetables, by the finding of various living creatures, 

 such as sponges, fungi, &c., possessing both the characters 

 of animals and vegetables. Even the division between 

 animate and inanimate is rapidly disappearing ; all bodies 

 being influenced by forces which change them, which alter 

 their structure, which differentiate them into new members, 

 new forms, or new compounds, or which disintegrate or 

 renew them ; even crystals, as well as vegetables and 

 animals, grow by natural selection and accretion, and 

 are also subject to abnormal formations ; and the action 

 of any force in any substance may be regarded as a 

 species of animation, vitality, or life. There is also no 

 definite line which separates vital from mental action. 

 In all departments of natural knowledge we are fast 

 being driven towards an universal system of unbroken 

 series of existences. 



The classifying of knowledge is a mental operation, 

 involving the comparison, selection, and permutation of 

 ideas ; it is also a logical process depending upon the 

 fundamental conceptions of identity and difference. In 

 classifying ideas we fix our attention upon and abstract 

 the similarity alone, and mentally disregard all other 

 circumstances, whether connected with it or not. The 



