168 THE GENESIS OF SCIEXCE. 



nite evidenco of progress. We know that the lever and 

 the mclined plane were employed during this period : im- 

 plying that there was a qualitative prevision of their effects, 

 though not a quantitative one. But we know more. We 

 read of weights in the earliest records ; and we find weights 

 in ruins of the highest antiquity. Weights imply scales, 

 of which we have also mention ; and scales involve the 

 primary theorem of mechanics in its least complicated form 

 — involve not a qualitative but a quantitative prevision of 

 mechanical effects. And here we may notice how mechan- 

 ics, in common with the other exact sciences, took its rise 

 from the simplest application of the idea of equality. For 

 the mechanical proposition which the scales involve, is, that 

 if a lever with equal arms, have equal weights suspended 

 from them, the weights will remain at equal altitudes. 

 And we may further notice, how, in this first step of ra- 

 tional mechanics, we see illustrated that truth awhile since 

 referred to, that as magnitudes of linear extension are the 

 only ones of which the equality is exactly ascertainable, the 

 equalities of other magnitudes have at the outset to be de- 

 termined by means of them. For the equahty of the 

 weights which balance each other in scales, wholly depends 

 upon the equality of the arms : we can know that the 

 weights are equal only by proving that the arms are equal. 

 And when by this means we have obtained a system of 

 weights, — a set of equal nnits of force, then does a science 

 of mechanics become j^ossible. Whence, indeed, it follows, 

 that rational mechanics could not possibly have any other 

 starting-point than the scales. 



Let us further remember, that during this same period 

 there was a limited knowledge of chemistry. The many 

 arts which we know to have been carried on must have 

 been impossible without a generalized experience of the 

 modes in wfeich certain bodies affect each other under spe- 

 cial conditions. In metallurgy, which was extensively 



