76 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



I am now speaking, the names of Seguin, Clausius, Helmholtz, Mayer, 

 and Colding on the Continent, and those of Grove, Joule, Eankine, 

 and Thomson in this country, will always be associated with this great 

 work. 



I must not, however, quit this subject without a passing notice of 

 a conclusion to which Sir William Thomson has come, and in which 

 he is followed by others who have pursued the transformation of 

 energy to some of its ultimate consequences. The nature of this will 

 perhaps be most easily apprehended by reference to a single instance. 

 In a steam engine, or other engine, in which the motive power de- 

 pends upon heat, it is well known that the source of power lies not in 

 the general temperature of the whole, but merely on the difference of 

 temperature between that of the boiler and that of the condenser. 

 And the effect of the condenser is to reduce the steam issuing from 

 the boiler to the same temperature as that of the condenser. When 

 this is once done, no more work can be got out of the engine, \mless 

 fresh heat be supplied from an outside source to the boiler. The heat 

 originally communicated to the boiler has become uniformly diffused, 

 and the energy due to that difference is said to have been dissipated. 

 The energy remains in a potential condition as regards other bodies ; 

 but as regards the engine, it is of no further use. Now suppose that 

 we regard the entire material universe as a gigantic engine, and that 

 after long use we have exhausted all the fuel (in ita most general 

 sense) in the world ; then all the energy available will have become 

 dissipated, and we shall have arrived at a condition of things from 

 which there is no apparent escape. This is what is called the ' Dis- 

 sipation of Energy.' 



Prof. Frankland has been so good as to draw up for 

 me the following account of the progress of Chemistry 

 during the last half-century. 



Most of the elements had been discovered before 1830, the 

 majority of the rarer elements since the beginning of the century. In 

 addition to these the following five have been discovered, three of 

 them by Mosander, viz. : lanthanum in 1839, didymium in 1842, 

 and ebrium in 1843. Ruthenium was discovered by Glaus in 1843, 

 and niobium by Rose in 1844. Spectrum analysis has added five to 

 the list, viz. : Ccesium and rubidium, which were discovered by 

 Bunsen and Kirchhoff in 1860; thallium, by Crookes in 1861 ; indium 



