+4$ POPULAR LECTURES AND ADDRESSES. 



and economically worked in the neighbourhood of 

 natural waterfalls. But the splendid suggestion 

 made about three years ago by Mr. Siemens (Sir 

 William Siemens) in his presidential address to the 

 Institution of Mechanical Engineers, that the power 

 of Niagara might be utilised, by transmitting it 

 electrically to great distances, has given quite a 

 fresh departure for design in respect to economy of 

 rain-power. From the time of Joule's experimental 

 electro-magnetic engines developing 90 per cent. 

 of the energy of a Voltaic battery in the form of 

 weights raised, and by the theory of the electro- 

 magnetic transmission of energy completed thirty 

 years ago on the foundation afforded by the train 

 of experimental and theoretical investigations 

 which established his dynamical equivalent of 

 heat in mechanical, electric, electro-chemical, 

 chemical, electro-magnetic, and thcrmoclastic phe- 

 nomena, it had been known that potential cm 

 from any available source can be transmitted 

 clcctro-magnctically by means of an electric cur- 

 rent through a wire, and directed to raise weights 

 at a distance, with unlimitedly perfect economy. 



