Buy Harmonium for Sale, Buy Harmonium Online. Harmonium is a keyboard instrument and is similar to a Reed Organ. It was invented in England around 1840 and then it gained popularity. Harmonium is also known as Peti or Baja. Harmonium is actually a bi-cultural instrument as the keyboard is European but drone reeds come from India. In Europe both foot-pumped and hand-pumped models are available but in India, only the hand-pumped model is used. Hence in India, the term harmonium refers to a hand-pumped instrument. These are mainly used for religious purposes (bhajans or kirtans).