  The concept of mechanical work is inherited from the concepts of potentia
absoluta and men's work, both implemented in the Section IX of Daniel
Bernoulli's Hydrodynamica in 1738. Nonetheless, Bernoulli did not confuse those
two entities: he defined a link from gender to species between the former,
general, and the latter, organic. Besides, Bernoulli clearly distinguished vis
viva and potentia absoluta (or work). Their mutual conversions are rarely
explicitly mentionned in this book, except once, in the Section X of his work,
from vis viva to work, and subordinated to the mediation of a machine, in a
driving forces substitution problem. His attitude significantly evolved in a
text in 1753, in which work and vis viva were unambiguously connected, while
the concept of potentia absoluta was reduced to the one of men's work, and the
expression itself was abandoned. It was then accepted that work can be
converted into vis viva, but the opposite is true in only one case, the
intra-organic one. The concept of tiredness, seen as an expenditure of animal
spirits conceived themselves as little tensed springs liberating vis viva,
allowed direct conversion, even never quantified and listed simply as a model,
from vis viva to work. Thus, work may have ultimately appeared as a
transitional state between two kinds of vis viva, which the first is
non-quantifiable. At the same time, natural elements were discredited from any
hint of profitable production. Only men and animals were able to work in the
strict sense of the word. Nature did not work by itself, according to
Bernoulli. Despite his will to bring together rational mechanics and common
mechanics, one perceived in the work of Bernoulli the subsistence of a rarely
crossed disjunction between practical and theoretical fields.
