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34. Note on the centres of similitude of a triangle of constant form circumscribed to a given triangle. London Math. Soc. Proc., xxiv, 1893, 369-72. 35. Note on a variable seven-points circle, analogous to the Brocard circle of a plane triangle. (ditto), xxv, 1894, 75-85. 36. Note on four special circles of inversion of a system of generalised Brocard circles of a plane triangle. (ditto), 376-88. 37. Note on some properties of a generalised Brocard circle, (ditto), xxvi, 1895, 173-183. 38. Note on the representation of a circle by a linear equation. (ditto), xxxii, 1900, 316-20. 20. ROBERT GRIFFITHS (1805-1883). Robert Griffiths, inventor of a screw propeller, was born at Lleweny Farm, in the Vale of Clwyd, on 13th December, 1805. He turned to the invention of various types of machinery and obtained patents for a rivet machine in 1835, a glass-grinding and polishing machine in 1836, and numerous others bearing on the manufacture of nuts and bolts. He removed from Birmingham to Havre, where, in conjunction with M. Labruere, he founded engineering works at which was manufactured most of the ironwork for the railway then being constructed from Havre to Paris. The French works had later to be closed down. Subsequently he experimented upon the screw pro- peller and in 1849 took out a patent for an amended method of screw propulsion. Further improvements were patented in 1853 and in 1858 and described before the Society of Naval Architects. Griffiths died in June, 1883. Source: D N B References to published works 1. On the propulsion of bodies through water. Naval Architects Trans., xvii, 1876, 252-6. 2. On the resistance given to screw-ships by the action of the screw- propeller, and how to remedy it. (ditto), xx, 1877, 104-14. 3. On the form of the stem and the arrangement of the propellers in screw-ships, in order to obtain the best effect in propulsion. United Service Inst. Journ., xxiii, 1880, 663-9.