Smithsonian Report, 1910. — Beyer. 



Plate 9. 



1. Mill Switch Board, Showing Method of Marking Electrical Equipment. 



The small sign at the top of the picture reading "Danger. — Keep away" is made of non- 

 conducting liber and is hung over a switch when anyone is working on the machinery 

 it controls. 



2. Protective Device for Trap Doors. 



Tlie guard rods rest on ledge of door frame 

 when the cover is raised, and drop down 

 out of the way when it is closed. 



3. Warning Sign to Attract Attention 

 TO Workmen Overhead. 



Intended to prevent injury from falling tools 

 or material. 



