246 report— 1879. 



But a full explanation of it is within the reach of any student who will train his 

 mind to reason consecutively, and avail himself of the aids to prolonged con- 

 secutive thought which mathematicians have contrived. He will then see that the 

 most ohvious and familiar mechanical facts involve as necessary consequences all 

 the phenomena which he finds in the schoolboy's top, in the physicist's gyroscope, 

 and in the precession and nutation of the heavens. This then is a problem of Nature 

 which falls within the province of the deductive method. 



Wherever data are known exactly, there inferences from these data however 

 remote may be depended upon as corresponding with what actually occurs in Nature. 

 And if in such cases the mind of man has proved equal to the task of drawing 

 inferences which can effectually grapple with the problems he finds around him in 

 the Universe — which is, alas ! as yet but too seldom — then will the deductive 

 method, our plummet, explore depths in the great ocean of existence which our 

 anchors of experiment could not have reached. 



The distinction which is here made between deductive and experimental inves- 

 tigations would have no place in a logical system. But it has direct reference to 

 human convenience, and derives its importance from this circumstance. It is 

 obvious, too, that an investigation may partake of both characters— that it may 

 require all the powers of the scientific observer to get at the facts, or even to ap- 

 preciate them, and all the resources of the mathematician to elicit the consequences 

 of them. For instance, on beginning his electrical studies, the student of Nature 

 must master a mixed experimental and deductive inquiry to get at the elementary 

 fact that free electricity resides either at or outside the surfaces of conductors ; 

 and he must engage in a further inquiry, and one only within the reach of a trained 

 mind, to deduce from this the law of the inverse square. And, again, no full 

 appreciation or even intelligent use of the common electrostatic and electrodynamic 

 measures which he meets at the threshold of his electrical studies is within the 

 reach of the mere experimentalist or of the mere theorist. And if this treacherous 

 ground lies before the immature student at his entrance, what shall we say of the 

 bogs he struggles into as he advances. We are perpetually meeting with inquiries 

 of this mixed character in electricity and some of the other physical sciences, but 

 they are comparatively rare in either mechanics or chemistry, and none that is 

 difficult lies in the path of the beginner. How many students are there who are 

 made to slur over the above and a multitude of similar difficulties, and who are 

 told that they are learning science, when in fact what they are really learning is 

 the pernicious habit of being content to see Nature through a fog or through other 

 men's mental eyes. 



In mechanics valuable progress can be made by the mere mathematician, the 

 student of deductive science ; and in chemistry similar progress can be made by the 

 mere experimentalist. Of all the physical sciences these are the most purely 

 deductive, and the most purely experimental. What I desire particularly to invite 

 attention to is that the two great methods of investigation may best be acquired in 

 these two sciences, and that for a really sound grasp of the remaining physical 

 sciences, and especially with a view to further advance in physical science, a com- 

 mand of both methods of investigation is essential. I ought to add, however, that 

 to confer this inestimable boon on the investigator of Nature, the great science of 

 mechanics must be studied by him in its own best form, and not degraded by the 

 vile expedient of evading the legitimate use of the infinitesimal calculus, to 

 comply, perhaps, with the ill-judged requirements of some examining body ; and 

 his practical chemistry must be the study of a science, and not a mere accumula- 

 tion of exercises in a lucrative art. 



We must bear in mind, too, that either method of investigation may be mis- 

 applied, and that this is a risk carefully to be guarded against. The deductive 

 method when misapplied lands us in speculation, the experimental method becomes 

 empiricism ; and it so happens that the sciences of mechanics and chemistry are not 

 pnly monuments of the power of the two great methods of investigation, but 

 instructive examples of their weakness also. For in chemistry, scarce any attempt 

 at prolonged reasoning, carrying us by any lengthened flight to a distance from 

 the experiments, can be relied on. The result has seldom risen to anything better 



