12 Dugald Clerk, The Work and Discoveries of Joule 



expected ; if the theory be in error, then the deductions prove 

 to be incorrect. 



The inductive method is supposed to have originated in 

 the mind of Roger Bacon, but it must have existed and been 

 used for many thousands of years before the thirteenth cen- 

 tury, because it was the method of trial and discovery of error 

 by experiment, the only method which dispensed with pure 

 theory while developing- inventions and contrivances for use 

 in attaining relative comfort and safety. Such applications 

 as fire to produce physical and chemical changes in matter 

 such as are involved in the manufacture of iron, copper, lead, 

 and other metals, or the production of oxides, such as quick- 

 lime, the operations of soap-making, glass-making, sulphuric 

 acid production, brewing, distilling, and dyeing, the inven- 

 tion of the wheel, spinning and weaving, have all been 

 developed by the method of trial followed by the correction 

 of errors arrived at experimentally. In fact, by induction 

 many experiments are made and definite knowledge of results 

 obtained even in the presence of erroneous theories. This 

 method enabled progress to be made before true theories were 

 developed. Thus the steam engine had been developed by 

 Newcomen, Smeaton, and James Watt, and applied to loco- 

 motion on sea and land as well as to the duties of driving 

 machinery and pumping water, long before any guiding 

 science of heat had come into existence. The engines were 

 mechanicallv excellent ; the fuel economy was good, and they 

 were built in units of thousands of horse-power. Steam 

 power, in fact, revolutionised the social and industrial condi- 

 tions of the globe ; but notwithstanding this great material 

 and engineering success, scientific men, like business men 

 and engineers, were equally in the dark as to the connection 

 between steam motive power and heat. It was seen that 

 motive power of almost any magnitude could be obtained by 

 the agency of heat ; but how it was obtained and how much 

 power was necessarily connected with a given quantity of 

 heat was quite unknown. Indeed, as we have seen, even Sir 

 William Thomson as late as 1848 was of opinion that there 

 was no mechanical equivalent of heat. Chemists were no 

 better informed than physicists ; they had only recently given 

 up the erroneous and terribly confusing idea of phlogiston 

 as an explanation of heat changes, although Lavoisier's work 

 in France had long proved the conservation of mass of matter 

 throughout such changes. It is true that the fuel consump- 

 tions of existing steam engines were known for given outputs 

 of mechanical work. Watt had long ago invented the steam 



