284 SIE ISAAC NEWTON. 



trivances, now forgotten, before he made the step which 

 created the engine anew, not only the Parallel Motion, possibly 

 a corollary to the proposition on circular motion in the 

 ' Principia,' but the Separate Condensation, and above all the 

 Governor, perhaps the most exquisite of mechanical inven- 

 tions ; and now we have those here present who apply the 

 like principle to the diffusion of knowledge, aware as they 

 must be, that its expansion has the same happy effect naturally 

 of preventing mischief from its excess, which the skill of the 

 great mechanist gave artificially to steam, thus rendering his 

 engine as safe as it is powerful. 



The grand difference, then, between one discovery or 

 invention and another is in degree rather than in kind ; the 

 degree in which a person while he outstrips those whom he 

 comes after, also lives as it were before his age. Nor can any 

 doubt exist that in this respect Newton stands at the head of 

 all who have extended the bounds of knowledge. The sciences 

 of Dynamics and of Optics are especially to be regarded in 

 this point of view ; but the former in particular ; and the 

 completeness of the system which he unfolded, its having been 

 at the first elaborated and given in perfection, its having, 

 however, now stood the test of time, and survived, nay gained 

 by the most rigorous scrutiny, can be predicated of this system 

 alone, at least in the same degree. That the calculus, and 

 those parts of dynamics which are purely mathematical, 

 should thus endure for ever, is a matter of course. But his 

 system of the Tiniverse rests partly upon contingent truths, 

 and might have yielded to new experiments, and more ex- 

 tended observation. Nay, at times it lias been thought to fail, 

 and further investigation was deemed requisite to ascertain if 

 any error had been introduced ; if any circumstance had 

 escaped the notice of the great founder. The most memor- 

 able instance of this kind is the dircrepancy supposed to have 

 been found between the theory and the fact in the motion of 

 the lunar apsides, which about the middle of the last century 

 occupied the three first analysts of the age.* The error was 

 * D'Alembert, Clairaut, Euler. 



