When one body combines with another in more than one proportion, the s — John Dalton

"Chemical analysis and synthesis go no farther than to the separation of particles one from another, and to their reunion. No new creation or destruction of matter is within the reach of chemical agency. We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen. All the changes we can produce, consist in separating particles that are in a state of cohesion or combination, and joining those that were previously at a distance."

"When we attempt to conceive the number of particles in an atmosphere, it is somewhat like attempting to conceive the number of stars in the universe; we are confounded with the thought. But if we limit the subject, by taking a given volume of any gas, we seem persuaded that, let the divisions be ever so minute, the number of particles must be finite; just as in a given space of the universe, the number of stars and planets cannot be infinite."

"Now it is one great object of this work, to shew the importance and advantage of ascertaining the relative weights of the ultimate particles, both of simple and compound bodies, the number of simple elementary particles which constitute one compound particle, and the number of less compound particles which enter into the formation of one more compound particle."

"Daltons records, carefully preserved for a century, were destroyed during the World War II bombing of Manchester. It is not only the living who are killed in war."

"Dalton, the mathematical tutor, following up the lead of Newton, combined the whole of the results of quantitative measurement which had accumulated up to his time, in a comprehensive theory, based on the concept of the chemical atom."

"He has shewn to us how vividly he formed these ideas, that they were no mere fancies which had passed through his brain, but distinct impressions, ready prepared for utterance. No doubt is left upon our minds as to his opinions, which are, that every piece of matter, even the smallest, must follow the laws of the largest; that when pounds of matter unite, the atoms contained in them must unite also, until we come to the fact that only atoms can really be said to unite. Now as the conception of any fraction of an atom is a contradiction and impossible, they must constantly unite as wholes, and the proportion will be constant. If constant in the smallest quantities, then so in the largest, explaining the permanency of the constitution of bodies so much disputed, and making it a law of nature. If two compound bodies unite, the same law is followed out."