A HISTORY OF SCIENCE 



cing figures." In this, air heated in a retort like a 

 miniature altar is allowed to escape through the sides 

 of two pairs of revolving arms precisely like those of 

 the ordinary revolving fountain with which we are ac- 

 customed to water our lawns, the revolving arms being 

 attached to a plane on which several pairs of statuettes 

 representing dancers are placed. An even more in- 

 teresting application of this principle of setting a wheel 

 in motion is furnished in a mechanism which must be 

 considered the earliest of steam-engines. Here, as the 

 name implies, the gas supplying the motive power is 

 actually steam. The apparatus made to revolve is a 

 globe connected with the steam-retort by a tube which 

 serves as one of its axes, the steam escaping from the 

 globe through two bent tubes placed at either end of an 

 equatorial diameter. It does not appear that Hero 

 had any thought of making practical use of this steam- 

 engine. It was merely a curious toy nothing more. 

 Yet had not the age that succeeded that of Hero been 

 one in which inventive genius was dormant, some one 

 must soon have hit upon the idea that this steam- 

 engine might be improved and made to serve a useful 

 purpose. As the case stands, however, there was no 

 advance made upon the steam motor of Hero for al- 

 most two thousand years. And, indeed, when the 

 practical application of steam was made, towards the 

 close of the eighteenth century, it was made probably 

 quite without reference to the experiment of Hero, 

 though knowledge of his toy may perhaps have given 

 a clew to Watt or his predecessors. 



In recent times there has been a tendency to give 

 to this steam-engine of Hero something more than 



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