410 ON THE FORCE OF MOISTURE 



But, unfortunately, this idea was not confirmed by experiment. 

 If the ascent of water, in a capillary tube, be intercepted, by cut- 

 ting the tube at half the height, for example, to which the water 

 ought to rise, the latter will not rise above the orifice to trickle 

 down the sides. And the case will be the same in the other at- 

 tempt. 



SECTION VI. 



On the force of Moisture in raising Burthens. 



One of the most singular phsenomena in physics, is the force 

 with which the vapour of water, or moisture, penetrates into those 

 bodies which are susceptible of receiving it. If a very considerable 

 burthen be affixed to a dry and well stretched rope, and if the 

 rope be only of .such a length as to suffer the burthen to rest 

 on the ground, on moistening the rope, you will see the burthen 

 raised up. 



The anecdote respecting the famous obelisk erected by Pope 

 Sixtus V. before St. Peter's #t Rome, is well known. The cheva- 

 lier Fontana, who had undertaken to raise this monument, was, it 

 is said, on the point of failing in his operation, just when the co- 

 lumn was about to be placed on its pedestal. It was suspended in 

 the open air, and as the ropes had stretched a little, so that the 

 base of the obelisk could not reach the summit of the pedestal, a 

 Frenchman cried out " Wet the ropes/' This advice was follow, 

 cd ; and the column, as if of itself, rose to the necessary height, to 

 be placed upright on the pedestal prepared for it. 



This story however, though often repeated, is a mere fable. 

 Those who read the description of the manoeuvres which Fontana 

 employed to raise his obelisk, will see that he had no need of such 

 assistance. It was much easier to cause his capstans to make a few 

 turns more, than to go in quest of sponges and water to moisten his 

 ropes. But the story is established, and will long be repeated in 

 France, because it relates to a Frenchman. 



However, the following is another instance of the power of mois- 

 ture, in overcoming the greatest resistances : it is the method by 

 which millstones are produced. When a mass of this stone has been 

 found sufficiently large, it is cut into the form of a cylinder, several 

 feet in height; and the question then is, how to cut it into hori- 

 zontal pieces, to make as many millstones. For this purpose, cir. 



