Warning: Undefined array key "visitor_referer_type" in /var/www/vhosts/wordinf.com/core/app/libraries/Core.php on line 98 Hermann von Helmholtz - Now, the external work of man...
Now, the external work of man is of the most varied kind as regards the force or ease, the form and rapidity, of the motions used on it, and the kind of work produced.