  This paper aims at shedding a new light on the novelty of Poincar\'e's
M\'ethodes nouvelles de la m\'ecanique c\'eleste. The latter's approach to the
three-body-problem has often been celebrated as a starting point of chaos
theory in relation to the investigation of dynamical systems. Yet, the novelty
of Poincar\'e's strategy can also be analyzed as having been cast out some
specific algebraic practices for manipulating systems of linear equations. As
the structure of a cast-iron building may be less noticeable than its creative
fa\c{c}ade, the algebraic cast of Poincar\'e's strategy was broken out of the
mold in generating the new methods of celestial mechanics. But as the various
components that are mixed in some casting process can still be detected in the
resulting alloy, this algebraic cast points to some collective dimensions of
the M\'ethodes nouvelles. It thus allow to analyze Poincar\'e's individual
creativity in regard with the collective dimensions of some algebraic cultures.
At a global scale, Poincar\'e's strategy is a testimony of the pervading
influence of what used to play the role of a shared algebraic culture in the
19th century, i.e., much before the development of linear algebra as a specific
discipline. This shared culture was usually identified by references to the
''equation to the secular inequalities in planetary theory.'' This form of
identification highlights the long shadow of the great treatises of mechanics
published at the end of the 18th century. At a more local scale, Poincar\'e's
approach can be analyzed in regard with the specific evolution that Hermite's
algebraic theory of forms impulsed to the culture of the secular equation.
Moreover, this papers shows that some specific aspects of Poincar\'e's own
creativity result from a process of acculturation of the latter to Jordan's
practices of reductions of linear substitutions within the local algebraic
culture anchored in Hermite's legacy .
