9 3 



LECTURES AND ESSA YS 



to withstand the pressure of the water ; 

 nor did he expect that his sacrifice would 

 cause the stream to roll back upon its 

 source and relieve him, by a miracle, of 

 its presence. But beyond the boundaries 

 of his knowledge lay a region where rain 

 was generated, he knew not how. He 

 was not so presumptuous as to expect a 

 miracle, but he firmly believed that in 

 yonder cloud-land matters could be so 

 arranged, without trespass on the miracu- 

 lous, that the stream which threatened 

 him and his people should be caused to 

 shrink within its proper bounds. 



Both these priests fashioned that 

 which they did not understand to their 

 respective wants and wishes. In their 

 case imagination came into play, uncon- 

 trolled by a knowledge of law. A 

 similar state of mind was long prevalent 

 among mechanicians. Many of these, 

 among whom were to be reckoned men 

 of consummate skill, were occupied a 

 century ago with the question of per- 

 petual motion. They aimed at con- 

 structing a machine which should execute 

 work without the expenditure of power ; 

 and some of them went mad in the 

 pursuit of this object. The faith in such 

 a consummation, involving, as it did, 

 immense personal profit to the inventor, 

 was extremely exciting, and every attempt 

 to destroy this faith was met by bitter 

 resentment on the part of those who 

 held it. Gradually, however, as men 

 became more and more acquainted with 

 the true functions of machinery, the 

 dreajn dissolved. The hope of getting 

 work out of mere mechanical com- 

 binations disappeared; but still there 

 remained for the speculator a cloud- 

 land denser than that which filled the 

 imagination of the Tyrolese priest, and 

 out of which he still hoped to evolve 

 perpetual motion. There was the mystic 

 store of chemic force, which nobody 

 understood ; there were heat and light, 

 electricity and magnetism, all competent 

 to produce mechanical motion. 1 Here, 



* See Helmholtz, Wechselwirkung der Natur- 

 krdfte. 



then, was the mine in which our gem 

 must be sought. A modified and more 

 refined form of the ancient faith revived ; 

 and, for aught I know, a remnant of 

 sanguine designers may at the present 

 moment be engaged on the problem 

 which like-minded men in former ages 

 left unsolved. 



And why should a perpetual motion, 

 even under modern conditions, be impos- 

 sible? The answer to this question is 

 the statement of that great generalisation 

 of modern science which is known under 

 the name of the Conservation of Energy. 

 This principle asserts that no power can 

 make its appearance in nature without 

 an equivalent expenditure of some other 

 power ; that natural agents are so related 

 to each other as to be mutually con- 

 vertible, but that no new agency is 

 created. Light runs into heat ; heat into 

 electricity ; electricity into magnetism ; 

 magnetism into mechanical force ; and 

 mechanical force again into light and 

 heat. The Proteus changes, but he is 

 ever the same ; and his changes in 

 nature, supposing no miracle to super- 

 vene, are the expression, not of spon- 

 taneity, but of physical necessity. A 

 perpetual motion, then, is deemed impos- 

 sible because it demands the creation 

 of energy, whereas the principle of Con- 

 servation is no creation, but infinite 

 conversion. 



It is an old remark that the law which 

 moulds a tear also rounds a planet. In 

 the application of law in nature the 

 terms "great" and "small" are unknown. 

 Thus the principle referred to teaches us 

 that the Italian wind, gliding over the 

 crest of the Matterhorn, is as firmly 

 ruled as the earth in its orbital revolution 

 round the sun ; and that the fall of its 

 vapour into clouds is exactly as much a 

 matter of necessity as the return of the 

 seasons. The dispersion, therefore, of 

 the slightest mist by the special volition 

 of the Eternal would be as much a 

 miracle as the rolling of the Rhone over 

 the Grirnsel precipices, down the valley 

 of Hasli to Meyringen and Brientz. 



It seems to me quite beyond the 



