Withney's Umbrella Withney was a mathematician who divided his time between mathematics and a career as a tightrope walker in a circus. Challenged one day by his manager to invent an umbrella with only two ribs, he created this object, which he began using in his acts. Alas, he died a few years later after falling onto the crowd. Some mathematicians, somewhat embarrassed to have a circus artist in their ranks, preferred subsequently to impose the word "cuspidal point" (in English "cusp").