82 THE SCIENTIFIC PAPERS OF 



exceeding 250 Fahr. on reaching the chimney, whereby great 

 economy in fuel is produced, with other advantages. 



The transfer of heat from the products of combustion to the air 

 and gas entering the furnace is effected by means of regenerators, 

 the principle of which has been recognised to some extent since 

 the early part of the present century, but has not hitherto been 

 carried out in any useful application in the arts, unless the respira- 

 tor invented by Dr. Jeffreys be so considered. The discovery of 

 this principle is ascribed to Rev. Mr. Stirling of Dundee, who in 

 conjunction with his brother, James Stirling, attempted as early 

 as the year 1817 to apply it to the construction of a hot-air 

 engine : their engine did not however succeed, nor did Captain 

 Ericsson's later attempts in the same direction lead to more satis- 

 factory results. The economical principle of the regenerator 

 having attracted the writer's attention in 1846, he constructed in 

 the following year an engine in which superheated steam was used 

 in conjunction with the regenerator : many practical difficulties 

 however prevented a realisation of the success which theory and 

 experiments appeared to promise ; but it is gratifying to find that 

 one principle then adopted, that of superheating the steam, has 

 since received the sanction of an extended application. 



The employment of regenerators for getting up a high degree 

 of heat in furnaces was suggested in 1857 by the writer's brother, 

 Mr. Frederick Siemens, and has since been worked out by them 

 conjointly through the several stages of progressive improvement. 

 The results obtained by the earlier applications of the principle 

 were communicated by the writer in a paper read at a former 

 meeting of this Institution (see Proceedings Inst. M.E., 1857, 

 page 103) * : and two or three of the furnaces then described, 

 employed for heating bars of steel, remain still in operation. In 

 attempting however to apply the principle to puddling and other 

 larger furnaces, serious practical difficulties arose, which for a con- 

 siderable time frustrated all efforts ; until by adopting the plan of 

 volatilising the solid fuel in the first instance, and employing it 

 entirely in a gaseous form for heating purposes, practical results 

 were at length attained surpassing even the sanguine expectations 

 previously formed. 



* Vide ante, p. 62. 



