THE ASTRONOMICAL VIEW OF NATURE. 313 



lier writers. Elaborate claims to priority have thus been 

 set up for persons to whom it is said the credit of modern 

 discoveries should be given. I do not intend to contribute 

 to this controversial literature, except by a general remark, 

 which will explain how it has come to pass that ideas and 

 principles now recognised as useful instruments of thought 

 and research have only recently attained this importance, 

 while they have frequently been the property of many 

 ages of philosophical thought, and familiar even to the 

 writers of antiquity. It is the scientific method, the exact 

 statement, which was wanting, and which raises the vague 

 guesses of the philosophical or the dreams of the poetic 

 mind to the rank of definite canons of thought, capable of 

 precise expression, of mathematical analysis, and of exact 

 verification. Obscure notions of the attractive and re- 

 pulsive forces of nature have floated before the minds of 

 philosophers since the time of Empedocles, but they did 

 not become useful to science till Galileo and Newton took 

 the first step to measure the intensity of those forces. 

 Lucretius's poem introduces to us the early speculations 

 on the atomic constitution of matter, but the hypotheses 

 of his school only led to real knowledge of the things of 

 nature when Dalton, following Lavoisier and Eichter, re- 

 duced this idea to definite numbers ; still more so when, 

 through the law of Avogadro and Ampere, and the calcu- 

 lations of Joule, Clausius, and Thomson, the velocities, the 

 number, and sizes of atoms became calculable and measur- 

 able quantities. Descartes, and after him Malebranche, 

 filled space with vortices which were to explain the con- 

 stitution of matter and the movements of its parts ; but 

 the notion was abandoned and ridiculed till Helmholtz 



