38 THE SEVEN FOLLIES OF SCIENCE 



There are several legitimate and successful methods of 

 obtaining a practically perpetual motion, provided we are 

 allowed to call to our aid some one of the various natural 

 sources of power. For example, there are numerous moun- 

 tain streams which have never been known to fail, and 

 which by means of the simplest kind of a water-wheel 

 would give constant motion to any light machinery. Even 

 the wind, the emblem of fickleness and inconstancy, may 

 be harnessed so that it will furnish power, and it does not 

 require very much mechanical ingenuity to provide means 

 whereby the surplus power of a strong gale may be stored 

 up and kept in reserve for a time of calm. Indeed this 

 has frequently been done by the raising of weights, the 

 winding up of springs, the pumping of water into storage 

 reservoirs and other simple contrivances. 



The variations which are constantly occurring in the 

 temperature and the pressure of the atmosphere have also 

 been forced into this service. A clock which required no 

 winding was exhibited in London towards the latter part 

 of the eighteenth century. It was called a perpetual 

 motion, and the working power was derived from variations 

 in the quantity, and consequently in the weight of the 

 mercury, which was forced up into a glass tube closed at 

 the upper end and having the lower end immersed in a 

 cistern of mercury after the manner of a barometer. It 

 was fully described by James Ferguson, whose lectures on 

 Mechanics and Natural Philosophy were edited by Sir 

 David Brewster. It ran for years without requiring wind- 

 ing, and is said to have kept very good time. A similar 

 contrivance was employed in a clock which was possessed 

 by the Academy of Painting at Paris. It is described in 

 Ozanam's work, Vol. II, page 105, of the edition of 1803. 



