2022-03-152022-03-151971https://hdl.handle.net/2152.3/11381First day cover featuring "Napier's Law," "Pythagorias' Law," "Boltzmann's Law," "De Broglie's Law," and "Archimedes' Law" stamps.First-day cover with five stamps from The Ten Mathematical Equations that Changed the Face of the Earth series. Issued by Nicaragua on May 15, 1971.First day covers (Philately)Stamp collectingPostage-stamp albumsNicaraguaAir mail envelopes