46 THE SEVEN FOLLIES OF SCIENCE 



the figure. The movable top of each receptacle has 

 affixed to it a weight, which shuts it in one situation and 

 opens it in the other. In the last place, the bellows of the 

 opposite arms have a communication by means of a canal, 

 and one of them is filled with quicksilver. 



" These things being supposed, it is visible that the bel- 

 lows on the one side must open, and those on the other 

 must shut ; consequently, the mercury will pass from the 

 latter into the former, while the contrary will be the case 

 on the opposite side." 



Ozanam natvely adds : " It might be difficult to point 

 out the deficiency of this reasoning ; but those acquainted 

 with the true principles of mechanics will not hesitate to 

 bet a hundred to one, that the machine, when constructed, 

 will not answer the intended purpose." 



That this bet would have been a perfectly safe one must 

 be quite evident to any person who has the slightest knowl- 

 edge of practical mechanics, and yet the fundamental idea 

 which is embodied in this and the other examples which we 

 have just given, forms the basis of almost all the attempts 

 which have been made to produce a perpetual motion by 

 purely mechanical means. 



The hydrostatic paradox by which a few ounces of liquid 

 may apparently balance many pounds, or even tons, has 

 frequently suggested a form of apparatus designed to secure 

 a perpetual motion. Dr. Arnott, in his " Elements of Phy- 

 sics," relates the following anecdote : "A projector thought 

 that the vessel of his contrivance, represented here (Fig. 9), 

 was to solve the renowned problem of the perpetual mo- 

 tion. It was goblet-shaped, lessening gradually towards 

 the bottom until it became a tube, bent upwards at c and 

 pointing with an open extremity into the goblet again. He 



