A HISTORY OF SCIENCE 



But if we find by experience that not only the thin 

 board, but every other figure of the same walnut-tree, 

 will return to float, as unquestionably we shall, then I 

 must desire my opponents to forbear to attribute 

 the floating of the ebony to the figure of the board, 

 since the resistance of the water is the same in rising 

 as in sinking, and the force of ascension of the walnut- 

 tree is less than the ebony's force for going to the 

 bottom. 



" Now let us return to the thin plate of gold or silver, 

 or the thin board of ebony, and let us lay it lightly 

 upon the water, so that it may stay there without 

 sinking, and carefully observe the effect. It will ap- 

 pear clearly that the plates are a considerable matter 

 lower than the surface of the water, which rises up 

 and makes a kind of rampart round them on every 

 side. But if it has already penetrated and overcome 

 the continuity of the water, and is of its own nature 

 heavier than the water, why does it not continue to 

 sink, but stop and suspend itself in that little dimple 

 that its weight has made in the water ? My answer is, 

 because in sinking till its surface is below the water, 

 which rises up in a bank round it, it draws after and 

 carries along with it the air above it, so that that 

 which, in this case, descends in the water is not only 

 the board of ebony or the plate of iron, but a com- 

 pound of ebony and air, from which composition re- 

 sults a solid no longer specifically heavier than the 

 water, as was the ebony or gold alone. But, gentle- 

 men, we want the same matter; you are to alter noth- 

 ing but the shape, and, therefore, have the goodness 

 to remove this air, which may be done simply by 



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