Anders Celsius magnitude (a measure of brightness) of certain stars. This was the first attempt to measure the intensity of starlight with a tool other than the human eye. He made observations of eclipses and various astronomical objects and published catalogues of carefully determined magnitudes for some 300 stars using his own photometric system (mean error=0.4 mag). Celsius was the first to perform and publish careful experiments aiming at the definition of an international temperature scale on scientific grounds. In his Swedish paper "Observations of two persistent degrees on a thermometer" he reports on experiments to check that the freezing point is
John Jones (astronomer) John Jones (astronomer) John Jones (18181898), also known as Ioan Bryngwyn Bach and Y Seryddwr ("The Astronomer"), was a Welsh amateur astronomer. He was born at Bryngwyn Bach, Dwyran, Anglesey, and received only an elementary education. From the age of twelve, he worked as a farm labourer. He later worked as a counter of cargoes of slate as they were loaded on to ships in Bangor, in modern Gwynedd. Unusually for someone of his background, he was not only a musician and a poet but proficient in several languages. He is noted mainly for his interest in astronomy: he constructed