Where can I find classic mathematical treatises?

[AdrianZ]

I'm looking for an English translation of Lagrange's treatise "Reflections on the algebric solutions of equations" (Reflexions sur la Resolution Algebrique des Equations). I've searched the internet for it but haven't found anything about it yet. Where can I find such truly classic treatises?

 

[mathwonk]

try eulers elements of algebra

 

[AdrianZ]

try eulers elements of algebra

I have that book. But I'm looking for langrange's method of finding symmetric polynomials for solving cubic and quartic equations. He has written a good treatise on that where he incompletely and probably unintentionally talks about Lagrange theorem in group theory.