31st Aug. 1864
Dear Sir
I think you misinterpret the third law of motion. Mathematically used to assure special qualities on the part of matter: in order to deal with mechanical questions they supposed bodies to be perfectly hard or perfectly elastic, but such bodies never occur in nature—Your target will not take up all the moving force of the ball—the quantity of vis viva2 possessed by the target after collision is less than the quantity possessed by the ball before collision, and the difference is immediately converted into heat. The whole of the vis viva is subsequently converted into heat. You set the target swinging, and this swinging is finally abolished by the resistance of the supports & of the air. When the target finally comes to rest; all the moving force, or vis viva possessed by the ball before collision has been converted into heat.
Yours very truly | John Tyndall
American Philosophical Society, Letter 7
Please cite as “Tyndall2131,” in Ɛpsilon: The John Tyndall Collection accessed on