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There is scarce any common mechanic trade, on the contrary, of

which all the operations may not be as completely and distinctly

explained in a pamphlet of a very few pages, as it is possible

for words illustrated by figures to explain them. In the history

of the arts, now publishing by the French Academy of Sciences,

several of them are actually explained in this manner. The

direction of operations, besides, which must be varied with every

change of the weather, as well as with many other accidents,

requires much more judgment and discretion, than that of those

which are always the same, or very nearly the same.