268 POPULAR SCIENCE MONTHLY 



THE DEVELOPMENT OF MECHANICS 



By S. E. SLOCUM, Ph. D. 



UNIVERSITY OF CINCINNATI 



HH HE history of mechanics affords a notable instance of what may be 

 ~ L called the relativity of science. In the course of its develop- 

 ment three distinct sets of mechanical principles have been formulated, 

 each having served in its turn as the foundation of a complete system 

 of mechanics. The first set of principles may be regarded as the first 

 mental image which man formed of the causes underlying the natural 

 motion of material bodies, and, although admirable in many respects, 

 was necessarily somewhat crude and naive. With increased mentality 

 came the formation of a new image, showing a greater maturity of 

 thought than the first and offering a more powerful method of analysis. 

 Finally, in recent times, a third image has been formed, which, although 

 not essentially different in content from the others, exhibits a greater 

 refinement of thought and expression. It is the purpose in what fol- 

 lows to outline briefly these three stages of development, and sketch 

 the chief characteristics of each. 



The first scientific development of mechanics arose from investi- 

 gations concerning the equilibrium and motion of the simple machines 

 in common use, such as the lever, inclined plane and pulley. This 

 order of development was inevitable for the twofold reason that these 

 implements had become familiar by centuries of use, and that they made 

 a direct appeal to the understanding through the grosser and more ele- 

 mentary sensations of weight and pressure. In the second century, 

 B.C., these investigations culminated in Archimedes's famous statement 

 of the principle of the lever, but for seventeen centuries thereafter this 

 statement remained the only instance of correct reasoning on natural 

 phenomena. Apparently human experience did not yet suffice to ex- 

 tend the interpretation of natural law, as witnessed by the Ptolemaic 

 system of astronomy, and Aristotle's division of motions into natural 

 and violent; a classification which served rather to obscure than 

 elucidate the subject. 



In the latter part of the fifteenth century a fresh start was made, 

 and the principle of the lever, handed down from Archimedes, was 

 further investigated and generalized by Guido Ubaldi and Leonardo 

 da Vinci. In 1586 these results were extended by Simon Stevin, 

 who, by hanging a string of fourteen balls over a triangular support, 

 established the properties of the inclined plane, and generalized his 



