Nicholas Griffin & Albert C. Lewis 
Collected Papers of Bertrand Russell, Volume 2 [PDF ebook] 
The Philosophical Papers 1896-99

The 1896-1899 papers, few of which were published in Russell’s lifetime, concentrate primarily on physics, arithmetic and the concept of quantity. Several views that later became well-known in his The Principles of Mathematics actually originate in his earlier work, and though incomplete, An Analysis of Mathematical Reasoning, forms a centrepiece of the volume.