384 ^h\ W. J. Macquoux R.vn'kine on the Science of Energetics. 



thetlcal bodies, such as the luminiferous tether ; sometimes to hypothetical 

 parts, whereof tangible bodies are conjecturally defined to consist, such as 

 atoms, atomic nuclei with elastic atmospheres, and the like. 



A mechanical hypothesis is held to have fulfilled its object, when, by 

 applying the known axioms of mechanics to the hypothetical motions and 

 forces, results are obtained agreeing with the observed laws of the classes 

 of phenomena under consideration, and when, by the aid of such a hypo- 

 thesis, phenomena previously unobserved are predicted, and laws antici- 

 pated, it attains a high degree of probability. 



A mechanical hypothesis is the better, the more extensive the range 

 of phenomena whose laws it serves to deduce from the axioms of me- 

 chanics ; and the perfection of such a hypothesis would be, if it could, 

 by means of one connected system of suppositions, be made to form a 

 basis for all branches of molecular physics. 



V. Advaitcages axd Disadta>tages of Hypothetical Theories. 



It is well known that certain hypothetical theories, such as the wave 

 theory of light, have proved extremely useful, by reducing the laws of a 

 various and complicated class of phenomena to a few simple principles, 

 and by anticipating laws afterwards verified by observation. 



Such are the results to be expected from well-framed hypotheses in 

 every branch of physics, Avhen used with judgment, and especially with 

 that caution which arises from the consideration, that even those hypo- 

 theses whose consequences are most fully confirmed by experiment, never 

 can by any amount of evidence attain that degree of certainty which be- 

 longs to observed facts. 



Of mechanical hypotheses in particular, it is to be observed, that their 

 tendency is to combine all branches of physics into one system, by making 

 the axioms of mechanics the first principles of the laws of all phenomena; 

 an object for the attainment of which an earnest wish was expressed by 

 Newton.* 



In the mechanical theories of elasticity, hght, heat, and electricity, 

 considerable progress has been made towards that end. 



The neglect of the caution already referred to, however, has caused 

 some hypotheses to assume, in the minds of the public generally, as well 

 as in those of many scientific men, that authority which belongs to facts 

 alone, and a tendency has consequently often evinced itself to explain 

 away, or set aside, facts inconsistent with these hypotheses, which facts, 

 rightly appreciated, would have formed the basis of true theories ; thus 



* Utinam cajtera naturae pliKiioraena ex principiis mechanicis eodem argumen- 

 tandi gencre dciivarc liceret.— (P/iiV. Nnl. Prin. Math. ; Pmf.) 



