the terms of the series are supposed to have a determinate qualitative meaning, and terms are disregarded, not because they are insignificant in magnitude, but because they are qualitatively insignificant; on the other hand, the omission itself ceases to have any place in the essential standpoint which, as regards the so called differential coefficient, acquires a specifically prominent position only with Lagrange, in the so called application of the calculus a point which will be discussed in detail in the following Remark.