wands, one held in each hand," and, more generally, as "an object that can be suspended on a string made taut by two held sticks". The Chinese yo-yo, often considered a type of diabolo, has been described as "a short round wooden stick with two round disks, 1.5 cm thick with a space between them, attached on either end of the stick...It will rotate on a string, each end tied to a thin stick," and as "two hollow discs of light wood, with openings in the sides, united by a peg tapering to its center". As with the yo-yo, the design of the diabolo has varied through history and across the world. Chinese diabolos have been made of bamboo. Wooden diabolos were common in Victorian times in Britain. Rubber diabolos were first patented by Gustave Philippart in 1905. In the late twentieth century a rubberised plastic material was first used. Metal has also been used, especially for fire diabolos. "Parker Brothers used steel for the bobbins [axles], with molded rubber ends, and also made some versions out of hollow Celluloid--which, because of its 'frictionless' properties, spun even faster than steel." Holes and metal strips alter the sound of the spinning diabolo, but create friction. The size and weight of diabolos varies. Diabolos with more weight tend to retain their momentum for longer, whereas small, light diabolos can be thrown higher and are easier to accelerate to high speeds. Rubber diabolos are less prone to breakage but are more prone to deformations. More commonly used are plastic-rubber hybrids that allow flex but hold their shape. The size of the disc or cone varies, as do the presence and size of holes in the discs or cones which may alter the sound produced. In yo-yos a cone is known as the butterfly shape. Regardless of the presence, size, and shape, "once a diabolo is spinning, the friction of the spinning diabolo against the string creates a whining sound; this is called 'making the diabolo sing.'" "When played hard, the [Chinese] yoyo will give out a sharp shrill sound...The shrill sound would add an exciting atmosphere to the [Shanghai winter] festivals...A skillful player can use a pot cover [with a round handle] as a yoyo [without sound]." A fast whirling kouen-gen produces "a shrill whistling sound...not unlike the note of the steam siren". Diabolos with only one cup ("monobolos") are also used. The