An incident which occurred in 1760 showed bow highly Euler was in general esteemed. The Russians having entered Brandenburg, advanced to Charlottenbure, and plundered a farm which belonged to Euler. When General Tottleben was informed who the proprietor was, he ordered immediate reparation to be made to an amount far above the injury, and the Empress Elizabeth presented him with 4000 florin& In consequence of his unceasing application to study, Euler had the misfortune to lose the eight of one eye in 1735, and in 1766 that of the other ; he however continued his valuable researches, some of his family acting as amanuensis, and his powers of memory are said to have been wonderfully increased even in his old age. He accepted the invitation of the Empress Catharine 11. of Russia to return to St. Paters burg in 1766, where he would have fallen a victim to an accidental fire which destroyed his house and property in 1771, but for the courageous efforts of a fellow-countryman (IL Grimon), who bore the old man away in his arms. Ilia manuscripts were saved by the exertions of Count Orloff.
On the 7th of September 1783, after some calculations on the motions of balloons, then newly invented, Euler dined with l,exell, and conversed on the lately-discovered planet Herschel. While playing with his grandchild, who was taking tea, he expired soddenly and without pain.
Euler was twice married in the same family, and had many children and grand-children ; his habit of life was strictly religious, the labours of each day being closed with a chapter from the Bible and family prayer. A catalogue of his published and unpublished writings is
given at the end of the 2nd volume of his ' Institutiones Calculi Differentialis; 1787; and to the first is prefixed an eloquent Elogo by Condoreet.
Every useful subject of mathematical research engaged at some thou the attention of Euler ; and for relaxation be amused himself with questions of pure curiosity, such as the knight's move in chess so as to cover all the squares. Ilis various researches have gone far towards creating the geometry of situation, a subject still imperfectly known. The following is one of the questions which Euler has gene ralised :—' At Kiinigburg, in Prussia, the river divides into two branches, with an island in the middle, connected by seven bridges with the adjoining shores; it was proposed to determine how a man should travel so as to pass over each bridge once and once only.' The memoirs of Euler are principally oontained io the following works Comment. Acad. Petrop.,' 1729-51 ; Novi Comment. Acad. Petrop,' 1750-76 ; ' Nova Acta Acad. Petrop.,' 1777-81; ' Mem. do l'Acad. des Sciences,' 1765-78 ; Receuil de l'Acad.,' 1727, &c. ; ' Miscell. BerolL,' tom. vii; 'Mem. de l'Acad. do Berlin,' 1745-67.