To the best of my knowledge neither the first nor the second editions of Scheel are presently available for download. I do have both in my collection, however.
I am pleased to inform both you and the assembled multitudes that the following IS available for download:
L'artillerie nouvelle depuis 1765 ou examen des changements faits dans l'artillerie franšaise by Charles Tronson du Coudray. Published in 1772. 288 pages: