There is opportunity for the exercise of considerable ingenuity and mechanical skill in developing automobile signaling apparatus, but the basis of any system or appliance of this nature that is destined to meet with lasting success is quite as much a matter of psychology as mechanics. No signaling apparatus can wholly succeed of its purpose unless two phases of the human equation have been properly considered. In order to serve its purpose as a warning, the signal must penetrate the wall of partial insensibility with which every human being unconsciously surrounds himself by directing his thoughts, along some particular line. Were the pedestrian fully aware of the dangers that beset him in the street, he would require no reminder of his peril. But his thoughts are elsewhere, and, for the moment, he is unconscious with respect to his surroundings. As there is a variation in the speed of perception and reaction in different individuals, the signal must be designed for its effect upon the least responsive of those who may still be termed normal.