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at Paris I ordered a carriage for the purpose of try¬ 
ing it, but I was called away by the sailing of my 
ship, before I could execute it. The object of it 
was to contrive some better springs for carriages^ 
than those now in use. Every body knows the u- 
tility of springs in saving the traveller from fatigue, 
and the carriage from being jolted to pieces ia 
rough roads. But it is not so generally known, 
that they enable a horse to go through his work 
with much less fatigue—could they therefore be 
adapted to farming carts, they would be found ex¬ 
tremely useful. The springs, of carriages now in 
use, are made either of wood, or iron. The first 
is too weak, or too clumsy ; the last is not only 
expensive, but heavy, and liable to rust, and above 
all, to snap in very cold weather. Springs of ei^ 
ther of these materials have one common and great 
inconvenience, that of not being able to adjust 
themselves to the different weights that are placed 
upon them. If they are so stiff as to bear a heavy 
burden, they have no elasticity under a light one^ 
or if they spring under a small pressure, they break 
under a heavy one. This circumstance greatly 
limits their utility. To wood and iron I would 
therefore substitute the lightest, the cheapest, and 
the most elastick of all substances— air. This 
can never break, and its spring will always be pro¬ 
portioned to the weight that it acts upon. Place a 
carriage box upon the pistons of four brass tubes, 
each containing twenty inches of air. If these 
were four inches deep, it would require 295ib, to 
