08 May The studies on sound and optics
The wave character of sound was elaborated on by Prastapada who hypothesized that sound was borne by air in increasing circles, similar to the movement of ripples in water.
Prastapada decribed the first sound as giving of a second, the second and third and so on expanding akasa in the same way as waves propogate themselves in water (bicitaranganyaya)
Susruta said that it was light arriving from an external source at the retina that illuminated the world around us. (This was reiterated by Aryabhatta).
Cakrapani suggested that both sound and light traveled in waves, but that light traveled at a much higher speed.
Others like the Mimamsakas imagined light to comprise of minute particles (now understood to be photons) in constant motion and spreading through radiation and diffusion from the original source.
Sound was understood to have its own reflection – pratidhvani (echo).
Musical pitches (sruti) were seen as caused by the magnitude and frequency of vibrations. A svara (tone) was believed to consist of a sruti (fundamental tone) and some anuranana (partial tones or harmonics).
Musical theory was elaborated on the basis of concepts such as jativyaktyoriva tadatamyam (genus and species of svara), parinama (change of fundamental frequency), vyanjana (manifestation of overtones), vivartana (reflection of sound), and karyakaranabhava (cause and effect of the sound).
Varahamihira discussed reflection as being caused by light particles arriving on an object and then back-scattering (kiranavighattana, murcchana). Vatsyayana referred to this phenomenon as rasmiparavartana, and the concept was adapted to explain the occurrence of shadows and the opacity of materials.
Refraction was understood to be caused by the ability of light to penetrate inner spaces of translucent or transparent materials and Uddyotakara drew a comparison with fluids moving through porous objects – tatra parispandah tiryaggamanam parisravah pata iti.
Varahamihira’s Panch Siddhanta holds a prominent place in the realms of astronomy. He proposed that the Moon and planets are lustrous not because of their own light but due to sunlight. It is acclaimed that Pancha Siddhantika of Varahamihira is one of the most important sources for the history of Hindu Astronomy from before the time of Aryabhata.