186 PHYSICAL SCIENCE IN THE MIDDLE AGES. 



CHAPTER I. 



On the Indistinctness of Ideas of the Middle Ages. 



THAT firm and entire possession of certain c.ear and distinct general 

 ideas which is necessary to sound science, was the character of 

 the minds of those among the ancients who created the several sciences 

 which arose among them. It was indispensahle that such inventors 

 should have a luminous and steadfast apprehension of certain general 

 relations, such as those of space and number, order and cause ; and 

 should be able to apply these notions with perfect readiness and pre- 

 cision to special facts and cases. It is necessary that such scientific 

 notions should be more definite and precise than those which common 

 language conveys ; and in this state of unusual clearness, they must be 

 so familiar to the philosopher, that they are the language in which he 

 thinks. The discoverer is thus led to doctrines which other men adopt 

 and follow out, in proportion as they seize the fundamental ideas, and 

 become acquainted with the leading facts. Thus Hipparchus, con- 

 ceiving clearly the motions and combinations of motion which enter 

 into his theory, saw that the relative lengths of the seasons were suffi- 

 cient data for determining the form of the sun's orbit ; thus Archimedes, 

 possessing a steady notion of mechanical pressure, was able, not only 

 to deduce the properties of the lever and of the centre of gravity, but 

 also to see the truth of those principles respecting the distribution of 

 pressure in fluids, on which the science of hydrostatics depends. 



With the progress of such distinct ideas, the inductive sciences rise 

 and flourish ; with the decay and loss of such distinct ideas, these 

 sciences become stationary, languid, and retrograde. When men 

 merely repeat the terms of science, without attaching to them any 

 clear conceptions ; — when their apprehensions become vague and dim ; 

 — when they assent to scientific doctrines as a matter of tradition, 

 rather than of conviction, on trust rather than on sight ; — when 

 science is considered as a collection of opinions, rather than a record 

 of laws by which the universe is really governed ; — it must inevitably 

 happen, that men will lose their hold on the knowledge which the 

 great discoverers who preceded them have brought to light. They 

 are not able to push forwards the truths on which they lay so 



