330 PERSONAL PREPARATION FOR RESEARCH. 



in a proper way, and with the aid of suitable expe- 

 riments, an instance* of chemical affinity with one of 

 mechanical mixture, we find that in the former the sub- 

 stances unite together in certain definite proportions by 

 weight, and produce a new , homogeneous body, widely 

 different in some of its properties from the original ones, 

 whereas in the latter the ingredients combine in no neces- 

 sarily fixed proportions, and the resulting body possesses 

 largely, in a mixed state, the properties of the original 

 substances. 



Great scientific insight, or the power of quickly 

 detecting essential resemblance and difference, and there- 

 by suggesting true hypothetical explanations, is a very 

 rare gift, and very important in original research ; some 

 men possess it in a remarkable degree. It may be culti- 

 vated by acquiring a ready knowledge of the chief groups 

 of natural phenomena, a familiar acquaintance with all the 

 known forces, and their general principles of action in 

 physical and chemical science, and by studying classified 

 and orderly series of scientific truths. For example, 

 physical and chemical phenomena are classed into those 

 of cohesion, simple mechanical action, sound, light, heat, 

 electricity, magnetism, and chemical force ; and sub- 

 stances according to their great divisions of simple and 

 compound, solid, liquid, and gaseous, their different sys- 

 tems of crystallisation, conductors and non-conductors of 

 sound, heat, and electricity, positive and negative bodies, 

 magnetic and dia-magnetic, thermo-electro-positive and 

 negative, metals and metalloids, chemical groups, monads, 

 dyads, triads, acids and bases, &c. The principles of 

 physical science are also divided into those of mechanical, 

 acoustic, optic, thermic, thermo-dynamic, magnetic, elec- 

 tric, magneto-electric, electro-magnetic, "magneto-optic, 

 chemical, and electro-chemical action, &c. Orderly series 



