In 1819, Gauss measured a degree of latitude between Gottingen and Altona. In geodesy he invented the heliotrope, by which the sunlight reflected from a mirror is used as a "sight" for the theodolite at a great distance. Through Professor William Weber he was introduced to the science of electro-magnetism, and they devised an experimental telegraph, chiefly for sending time signals, between the Observatory and the Physical Cabinet of the University. The mirror receiving instrument employed was the heavy prototype of the delicate reflecting galvanometer of Sir William Thomson. In 1834 messages were transmitted through the line in presence of H.R.H. the Duke of Cambridge; but it was hardly fitted for general use. In 1883 (?) he published an absolute system of magnetic measurements. On July 16, 1849, the jubilee of Gauss was celebrated at the University; the famous Jacobi, Miller of Cambridge, and others, taking part in it. After this he completed several works already begun, read a great deal of German and foreign literature, and visited the Museum daily between eleven and one o'clock. In the winters of 1854-5 Gauss complained of his declining health, and on the morning of February 23, 1855, about five minutes past one o'clock, he breathed his last. He was laid on a bed of laurels, and buried by his friends. A granite pillar marks his resting-place at Gottingen. II. WILLIAM EDWARD WEBER. WILLIAM EDWARD WEBER was born on October 24, 1804, at Wittenberg, where his father, Michael Weber, was professor of theology. William was the second of three brothers, all of whom were distinguished by an aptitude for the study of science. After the dissolution of the University of Wittenberg his father was transferred to Halle in 1815. William had received his first lessons from his father, but was now sent to the Orphan Asylum and Grammar School at Halle. After that he entered the University, and devoted himself to natural philosophy. He distinguished himself so much in his classes, and by original work, that after taking his degree of Doctor and becoming a Privat-Docent he was appointed Professor Extraordinary of natural philosophy at Halle.