Euler was the master in analysisng anything. This can be seen in his words in the preface of his book "Mmathematica" (translated by Ian Bruce), where he speaks on the text of Hermann "Phoronomiam": Euler has given many insightful words on analysisng things in his preface of many other books, another piece of statements of interest would be of his statements in the preface of "Introduction to Analysis of the infinite" (English translated verstion of Blanton). All the above indicates his personlaity of not leaving anything unresolved, consider the following passage from his book "Foundations of Differential Calculus" (English vesion of Blanton translation): As I am beginner in understanding there differentials, I don't understand him. At one place, he says differentials to be "vanishing" increments or "nothing" quantities, and in the other place he says it to be "infinitely small". Is there any other fragment of statements where Euler has analysed the concept of "differentials" properly, or is there any different meaning that can be given to the above statements to understand them? I am still reading this book, so I don't know whether he has analysed later on, if it is the case, I will report, but until then, I want to know whether anyone has idea on his stand on this concept; papers or books on this matter by Euler or any other person would be really helpful. I think differentials to be closely related to infinitesimals, so I want know Eulers analysis on both of them (if they are different).