Vintage DIY Critical Thinking Game: Nine Men's Morris, or Shepherd's Game/Project Gutenberg

See page 283 here.

The Eclectic School Geometry/Google Books

Title The Eclectic School Geometry
Authors Evan Wilhelm Evans, James Jesse Burns
Publisher Amer. Book Co., 1884
Length 149 pages
Click here.

First Steps in Geometry/Google Books

First steps in geometry
Authors George Albert Wentworth, George Anthony Hill
Publisher Ginn & company, 1901
Length 156 pages
Overview

The First Steps in Algebra/Google Books

The first steps in algebra
Author George Albert Wentworth
Publisher Ginn & company, 1908
Length 233 page
Overview

Wentworth & Hill's Examination Manual, Issue 1(Arithmetic)/Google Books

No answer booklet, just test. Appears to cover elementary school and early middle school mathematics, and probably proceeds, School Arithmetics(Grades 7 and 8).

Wentworth & Hill's examination manuals, Issue 1
Authors George Albert Wentworth, George Anthony Hill
Publisher Ginn & Co., 1894
Overview

School Arithmetics(Grades 7 and 8)/Google Books

School arithmetics
Wentworth-Smith mathematical series
School Arithmetics, George Albert Wentworth
Book 3 of School arithmetics: book one-three
Authors George Albert Wentworth, David Eugene Smith
Publisher Ginn, 1920
Overview

Solid Geometry/Google Books

Solid geometry
Wentworth-Smith mathematical series
Authors George Albert Wentworth, David Eugene Smith
Publisher Ginn and Company, 1913
Length 191 pages
Overview

Elementary geometry, plane and solid: for use in high schools and academies/Google Books

Elementary geometry, plane and solid: for use in high schools and academies
Author Thomas Franklin Holgate
Publisher The Macmillan company, 1901
Length 440 pages
Overview

A Text-book of Geometry /Google Books

A text-book of geometry
Author George Albert Wentworth
Publisher Ginn & Co., 1890
Length 437 pages

Overview here.

Computing Tables and Mathematical Formulas/Google Books

Overview

Computing Tables and Mathematical Formulas: Arranged for the Use of High Schools and Colleges
Author Eugene Henry Barker
Publisher Ginn and company, 1913
Length 88 pages

A History of Mathematics/Google Books

A history of mathematics
By Florian Cajori
Published by Macmillan & Co., 1893
422 pages

Begin reading here.

Main page.

This would be appropriate for advanced high school students

Free Math Courses Online

Not free ebooks, but math can be a tricky subject to teach(and expensive), so I thought I'd link this here. The Education Portal has a nice list of colleges, universities and other learning centers offering free math courses online and software. Click here.

A Primer of Calculus/Internet Archives

Click here.

Shop Mathematics/Google Books

Shop Mathematics
By John Michael Christman
Published by Macmillan, 1922
321 pages

Main page
Begin reading here.

Business Mathematics/Google Books

Click here to begin reading.

Main page
Business Mathematics: A Textbook for Schools
By Edward Ira Edgerton, Wallace Edgar Bartholomew
Published by The Ronald press company, 1921
305 pages

Vocational Mathematics for Girls/Google Books

Politically incorrect math for girls. ;) This book covers: household budgets, kitchen math, dress making, thrift and investment, farm math, and math in formally traditional female occupations outside the home.

Begin reading here.
Main page.

Vocational Mathematics for Girls

By William Henry Dooley

Published by D.C. Heath & co., 1917

369 pages

May or may not be useful for homeschool math, but it is interesting for cultural/history studies.

A High-school Astronomy /Google Books

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Main page
A High-school Astronomy: In which the Descriptive, Physical, and Practical are Combined : with Special Reference to the Wants of Academies and Seminaries of Learning
By Hiram Mattison
Published by Mason Bros., 1857
240 pages

Grammar School Algebra/Google Books

Click here.
Grammar School Algebra
By George Edward Atwood
Published by Morse Co., 1900
253 pages

Covers mathematical concepts to approximately the sixth grade.

Complete Graded Arithmetic Sixth Grade/Google Books

Click here.

Answers included. Note: Google's page numbers do not correspond to book page numbers - title page begins on page 399.

Complete Graded Arithmetic Seventh Grade /Google Books

Click here.