SOME EARLY CONTRIBUTIONS TO THE HISTORY OF GEOMAGNETISM—V

Abstract

As the fifth contribution in our series of early documents pertaining to geomagnetism, we are privileged to publish a translation of “Estromento de Sombras” (1537) by Pedro Nunes as reproduced by Hellmann in this Rara Magnetica. This is a section of the extremely rare book “Tratado da Sphera com a Theorica do Sol e da Lua”1 in which Nunes describes an improvement to Guillen's instrument (brújula de variación) consisting of the addition of a device permitting the observation of the Sun's altitude. He also gives a new method of determining the latitude at any hour of the day.We are under deep obligation to Dr. J. de Sampaio Ferraz of Rio de Janeiro for the following translation of “Estromento de Sombras.” Dr. Sampaio Ferraz also informs us that there is a copy of the rare “Tratado da Sphera com a Theorica do Sol e da Lua” in the Biblioteca Nacional at Rio de Janeiro. His comparison of the two texts showed that the edition in Rio de Janeiro, published at Lisbon in 1537, differs only in a few minor orthographical details from the text as reproduced by Hellmann.