English: Drawing of a powerful electromagnet used in physics laboratories built by H. du Bois, from around 1910. The large curved cylinders on each side are the windings, which are connected to a source of DC electricity through the terminals visible at the base of each winding. The pole pieces visible in the center are conical shaped to concentrate the magnetic field. The shafts projecting from the curved sides are hand screws which hold the pole pieces on, so different shaped pole pieces can be attached. The accompanying text says only "An excellent form of electromagnet for production of very powerful fields has been designed by H. du Bois (fig.6)." Alterations to image: Converted image to greyscale to eliminate reddish-brown tint of background (probably due to aging of paper stock), increased brightness of background to white to get rid of JPEG artifacts, converted JPEG to 32 grayscale PNG.