THE LOCOMOTIVE OBTRUSIVE. 2t 



The condensing engine, however, contributed to the 

 discovery of the mechanical origin of heat, in that it led to 

 the recognition of work as the measure of mechanical action ; 

 and to the locomotive must be attributed the birth of that 

 philosophical interest respecting heat and work which 

 immediately followed its general introduction. The con- 

 densing engine had not been obtrusive — it was not generally 

 to be seen unless looked for. The locomotive is obtrusive ; 

 it will be seen: and by 1842 locomotives had obtruded 

 themselves pretty well all over Europe. They immediately 

 took their places as objects of as much wonder and interest 

 to the grown people who saw them for the first time as they 

 are still to the young ; demanding the attention even of 

 philosophers who had previously studied nothing lower 

 than the planets. It thus turned out, as became known 

 some eight years after, that about this time three philo- 

 sophers, Seguin (1839), Mayer (1842), and Colding (1843), 

 suggested, as the result of philosophical reasoning, that 

 heat is convertible into mechanical effect. 



But it was not by such suggestions that the prejudice 

 and casuistry respecting caloric were to be removed. Even 

 had these suggestions met with general acceptance, had the 

 •convertibility of heat into mechanical effect been recognized 

 at the time, it does not follow that the result would have 

 been the general recognition of the conservation of energy. 

 Besides mechanical effect, there were the other physical 

 effects which result in combustion and the passage of 

 electricity in conductors, by which heat is produced or 

 developed, as it was then called, and these were then even 

 less understood. And although Mayer followed up his first 

 suggestion by developing many of its more important 

 consequences, his work attracted little notice and carried 

 no conviction. 



