Triangle — Chambers's Encyclopaedia

Triangle, a musical instrument of percussion, formed of a steel rod bent in triangle-form, open at one angle, as shown in the figure. It is suspended by means of a string attached to the upper angle, and struck with a steel beater ( $\alpha$ in figure). Many composers use it in their works as an adjunct to the drums, and it has a place in all military bands.

Diagram of a triangle-shaped percussion instrument, likely a triangle. It is a bent metal rod with an open angle at the top. A string is attached to the upper angle, and a small vertical rod labeled alpha is shown as a beater.