Verhulst, F. Perturbation theory from Lagrange to Van der Pol. (English) Zbl 0567.01001 Nieuw Arch. Wiskd., IV. Ser. 2, 428-438 (1984). This is a technical article indicating those aspects of modern perturbation theory that were first developed by Clairaut and later extended by Lagrange, Laplace and van der Pol. Van der Pol developed a theory of nonlinear oscillations for vibrations in triodes which has applications to the theory of planetary perturbations. The author demonstrates that van der Pol was fully aware of the relationship between his theory of triodes and celestial mechanics. Reviewer: Th.Hankins MSC: 01A05 General histories, source books 34-03 History of ordinary differential equations 85-03 History of astronomy and astrophysics 34C25 Periodic solutions to ordinary differential equations 34E10 Perturbations, asymptotics of solutions to ordinary differential equations 70-03 History of mechanics of particles and systems 70F15 Celestial mechanics Keywords:Clairaut; Laplace; nonlinear oscillations; planetary perturbations; celestial mechanics Biographic References: Lagrange, J. L.; Van der Pol, B. PDFBibTeX XMLCite \textit{F. Verhulst}, Nieuw Arch. Wiskd., IV. Ser. 2, 428--438 (1984; Zbl 0567.01001)