ed these into classes and species. His six
orders were _recepteurs_ (receivers of motion from the prime mover),
_communicateurs_, _modificateurs_ (modifiers of velocity), _supports_
(e.g., bearings), _regulateurs_ (e.g., governors), and _operateurs_,
which produced the final effect.[65]

[Footnote 65: Giuseppe Antonio Borgnis, _Theorie de la mecanique
usuelle_ in _Traite complet de mecanique appliquee aux arts_, Paris,
1818, vol. 1, pp. xiv-xvi.]

The brilliant Gaspard-Gustave de Coriolis (1792-1843)--remembered mainly
for a paper of a dozen pages explaining the nature of the acceleration
that bears his name[66]--was another graduate of the Ecole Polytechnique
who wrote on the subject of machines. His book,[67] published in 1829,
was provoked by his recognition that the designer of machines needed
more knowledge than his undergraduate work at the Ecole Polytechnique
was likely to give him. Although he embraced a part of Borgnis'
approach, adopting _recepteurs_, _communicateurs_, and _operateurs_,
Coriolis indicated by the title of his book that he was more concerned
with forces than with relative displacements. However, the attractively
simple three-element scheme of Coriolis became well fixed in French
thinking.[68]

[Footnote 66: Gaspard-Gustave de Coriolis, "Memoire sur les equations du
mouvement relatif des systemes de corps," _Journal de l'Ecole
Polytechnique_, 1835, vol. 15, pp. 142-154.]

[Footnote 67: Gaspard-Gustave de Coriolis, _De Calcul de l'effet des
machines_, Paris, 1829. In this book Coriolis proposed the now generally
accepted equation, work = force x distance (pp. iii, 2).]

[Footnote 68: The renowned Jean Victor Poncelet lent weight to this
scheme. (See Franz Reuleaux, _Theoretische Kinematik: Grundzuege einer
Theorie des Maschinenwesens_, Braunschweig, 1875, translated by
Alexander B. W. Kennedy as _The Kinematics of Machinery: Outlines of a
Theory of Machines_, London, 1876, pp. 11, 487. I have used the Kennedy
translation in the Reuleaux references throughout the present work.)]

Michel Chasles (1793-1880), another graduate of the Ecole Polytechnique,
contributed some incisive ideas in his papers on instant centers[69]
published during the 1830's, but their tremendous importance in
kinematic analysis was not recognized until much later.

[Footnote 69: The instant center was probably first recognized by Jean
Bernoulli (1667-1748) in his "De Centro Spontaneo Rotationis" (_Johannis
Bernoulli .