1. "A Survey Of Modern Algebra" by G.Birkhoff and S.MacLane, Chapters I, II, and III
The pdf copy of the book is provided by lisabeckphotography.com and can be found there.
2. "What Is Mathematics?" by R.Courant and H.Robbins, Chapters I and II
3. "Number, the Language of Science" by T.Dantzig
Freely downloadable from the online resource engineering108.com by clicking on the link.
4. "Infinity" by L.R.Lieber, pp. 87-203
The digital edition can be obtained free of charge from arcaneknowledgeofthedeep.files.wordpress.com by following the link.
5. "Higher Algebra for the Undergraduate" by M.K.Weiss, Chapters I and II
The book can be bought for as much as 3$ on Amazon.
6. "Philosophy of Mathematical and Natural Science" by H.Weyl, Chapter II
7. "An Introduction to Mathematics" by A.N.Whitehead, Chapters V-VIII
The work is in the public domain.
The following articles from American Mathematical Monthly are definitely worth reading:
1. "On Proofs by Mathematical Induction" by E.T.Bell
The article in pdf can be acquired from arXive.com there.
2. "Definitions of Imaginary and Complex Numbers" by E.S.Allen
The resource can be accessed there.
3. "An Early Reference to Division by Zero" by C.B.Boyer
The jstor copy can be downloaded through this link.
4. "Historical Note on the Graphic Representation of Imaginaries before the time of Wessel" by F.Cajori
The pdf copy is published online.
5. "Mathematical Induction" by G.E.Raynor
The article can be read online free of charge on jstor.
