Full Idea
If an infinite line be measured out in feet, it will consist of an infinite number of such parts; it would equally consist of an infinite number of parts, if each part was only an inch; therefore, one infinity would be twelve times as great as the other.
Gist of Idea
An infinite line can be marked in feet or inches, so one infinity is twelve times the other
Source
Baruch de Spinoza (The Ethics [1675], I Pr 15)
Book Reference
Spinoza,Benedict de: 'Ethics, Improvement of Understanding, Letters', ed/tr. Elwes,R [Dover 1955], p.56
A Reaction
This seems to anticipate Cantor. Spinoza's point seemed bewildering then, but is now accepted as a standard feature of the concept of infinity.