Hoffmann (Professor), 1839-1919., Plate, Adrian, inscriber., Harry Houdini Collection (Library of Congress) · New York : E.P. Dutton & Co. ; London : George Routledge & Sons, 1904. · leaf 71
, in the form Fic. 38. above described, its utility is extremely questionable. If the direction of the cord is through it in a straight line, a guide is obviously unnecessary. If, on the other hand, the cord enters or leaves the tube at an angle, friction must necessarily be created, varying in… … Fig. 39. tion of the cord. In default of ivory, a similar ring of bone or brass may be used with very little sacrifice of practical effectiveness; but ivory is the ideal material where friction is to be avoided. Another ingenious anti-friction contrivance, in-