[146] Dr. WHEWELL, ON THE TRANSFORMATION OF HYPOTHESES, &c. 



account for all the phenomena on the emission theory ; with this limitation only, that the 

 emission will have no share in the explanation, and the undulations will have the whole. 

 If, instead of conceiving the universe full of a stationary ether, we suppose it to be full 

 of etherial particles moving in every direction ; and if we suppose, in the one case and 

 in the other, this ether to be susceptible of undulations proceeding from every luminous 

 point ; the results of the two hypotheses will be the same ; and all we shall have to say 

 is, that the supposition of the emissive motion of the particles is superfluous and useless. 



6. This view of the manner in which rival theories pass into one another appears to be 

 so unfamiliar to those who have only slightly attended to the history of science, that I have 

 thought it might be worth while to illustrate it by a few examples. 



It might be said, for instance, by such persons, " Either the planets are not moved by 

 vortices, or they do not move by the law by which heavy bodies fall. It is impossible that 

 both opinions can be true." But it appears, by what has been said above, that the Cartesians 

 did hold both opinions to be true; and one with just as much reason as the other, on their 

 assumptions. It might be said in the same manner, " Either it is false that the planets are 

 made to describe their orbits by the above quasi-Cartesian theory of Bernoulli, or it is false 

 that they obey the Newtonian theory of gravitation." But this would be said quite errone- 

 ously ; for if the hypothesis of Bernoulli be true, it is so because it agrees in its result with 

 the theory of Newton. It is not only possible that both opinions may be true, but it is 

 certain that if the first be so, the second is. It might be said again, " Either the planets 

 describe their orbits by an inherent virtue, or according to the Newton theory." But this again 

 would be erroneous, for the Newtonian doctrine decided nothing as to whether the force of 

 gravitation was inherent or not. Cotes held that it was, though Newton strongly protested 

 against being supposed to hold such an opinion. The word inherent is no part of the physical 

 theory, and will be asserted or denied according to our metaphysical views of the essential 

 attributes of matter and force. 



Of course, the possibility of two rival hypotheses being true, one of which takes the expla- 

 nation a step higher than the other, is not affected by the impossibility of two contradictory 

 assertions of the same order of generality being both true. If there be a new-discovered comet, 

 and if one astronomer asserts that it will return once in every 20 years, and another, that it 

 will return once in every 30 years, both cannot be right. But if an astronomer says that 

 though its interval was in the last instance 30 years, it will only be 20 years to the next 

 return, in consequence of perturbation and resistance, he may be perfectly right. 



And thus, when different and rival explanations of the same phenomena are held, till one 

 of them, though long defended by ingenious men, is at last driven out of the field by the pres- 

 sure of facts, the defeated hypothesis is transformed before it is extinguished. Before it has 

 disappeared, it has been modified so as to have all palpable falsities squeezed out of it, and 

 subsidiary provisions added, in order to reconcile it with the phenomena. It has, in short, 

 been penetrated, infiltrated, and metamorphosed by the surrounding medium of truth, before 

 the merely arbitrary and erroneous residuum has been finally ejected out of the body of per- 

 manent and certain knowledge. 



W. W. 



Trinity Lodge, 



April 15, 1851. 



