He considered linear equations with constant coefficients, second order differential equations with variable coefficients, power series solutions of differential equations, a method of variation of constants, integrating factors, a method of approximating solutions, and many others.
Siya ang itinuturing na guhit equation na may pare-pareho coefficients, second-order ng kaugalian equation na may variable coefficients, kapangyarihan ng serye ng mga solusyon sa kaugalian equation, isang paraan ng pagkakaiba-iba ng mga constants, pagsasama ng mga kadahilanan, ang isang paraan ng approximating solusyon, at maraming iba pa.