So I decided to start reading Jevons' text book on Logic and on page 2 he says,
"In chemistry the law of equivalent proportions describes the well ascertained fact that each chemical substance enters into combination with every other chemical substance only in certain definite as when exactly eight parts by weight of oxygen unite with one part of hydrogen to form water..."
Huh? Now, I know I am splitting hairs here (and it is largely inconsequential to the topic but, H2O is water, right? As in 2 parts (weights?) of Hydrogen unite with one part (weight?) of Oxygen to form water? Am I misunderstanding the lingo here, was the chemical makeup of water just wrong back when Jevons wote this little tome?
"If men are not angels, then who shall run the state?"
He's talking about the proportions of the mass of the elements in water.
http://en.wikipedia.org/wiki/Law_of_definite_proportions
The atomic weight of oxygen is about 16. The atomic weight of hydrogen is about 1. 2x hydrogen is 2, or one part of H2O (by weight). Whereas 1x oxygen is 16, or eight parts of H2O (by weight).