पारदयन्त्रम् — Mercury in Bhoja's Machines

Mercury (pārada, rasa, "the king of fluids") appears in the most famous verses of chapter 31 of the Samarāṅgaṇasūtradhāra: a great bird of light wood with a "mercury-machine" (rasa-yantra) in its belly and a fire beneath it (31.95–96); a wooden aerial car carrying four strong vessels filled with mercury, heated over iron pans, which "becomes the ornament of the sky" (31.97–98); and an iron vessel of mercury, heated and set on a high place, that roars like a lion and drives elephants away (31.99–100). Earlier in the chapter Bhoja also explains why mercury is not a fifth seed of machines (31.6–8). This article presents these verses and reads them against the physical properties of mercury. Mercury is very dense, expands evenly when heated, boils at 357 °C and gives off toxic vapour. Heated in a closed iron vessel it can expand, boil violently and make a loud noise: Bhoja's roaring vessel is physically plausible. But heated mercury cannot make anything fly. The flying devices are discussed in detail in Article 12; here the question is simply what mercury could and could not contribute. The article also places the verses in the context of Indian rasaśāstra, in which mercury was the central substance, and notes the textual uncertainties. Article 10 of the series Yantravidhāna Studies (SSD-31), on chapter 31 of Bhoja's Samarāṅgaṇasūtradhāra. Verses discussed: 31.6–8, 31.95–100. Web version: sanskritmanthan.in/a/ssd-31-10-parada-yantra