OTAGO INSTITUTE

Otago Witness, Issue 3215, 27 October 1915, Page 3

OTAGO INSTITUTE

TECHNOLOGICAL BRANCH'. The last of the meetings of the Technological branch of the Otago Institute for the current year was held in the physics room, Otago University, on the 19th, when the annual meeting was held and a lecture was delivered by Professor J. Park on “Strength of Materials.” Mr J. Blair Mason occupied the chair. ANNUAL MEETING. The report stated that the year just closed was the fifth of, the existence of the branch. Despite tho distraction of the war and the inevitable absence of many members at the front and elsewhere, good and useful meetings had been held, with profit _ and satisfaction to those who had participated in them. An innovation adopted by the committee had been the restriction of the meetings to the winter months. It had not been thought advisable to attempt to continue the annual dinner for the present. The adoption of the report and balance sheet, which showed the branch to be _ in a flourishing condition, the balance being over £lB, w r as moved by the Chairman and carried. The sum of £lO was voted to the funds of the Astronomical branch. The following office-bearers were elected: President, Mr J. Blair Mason; vice-chair-men —Professor J. Park, Professor D. B. Waters, and Mr B. B. Hooper; committee — Messrs G. W. Davies, W. D. R. M'Curdie, George Simpson, R. N. Vanes, and Mandeno ; secretary, Mr H. Brasch. LECTURE. Professor Park first dealt with the theoretical conditions underlying the strength and design of structures, and later with the application of first principles, on which, he said, all engineering practice depended. The strength of material lay in its ability to resist deformation under the influence of an external force. In the case of bridges there were two forces to be considered: dead weight, including that' of the bridge itself and any load applied suddenly and causing vibration —a live load. A live load would be such as a train in motion, and such a load imposed at least double the stress that would be set up by a dead load of the same magnitude. The lecturer defined the terms stress and strain, the former signifying the force or forces acting on a body, and strain tho change of shape resulting from stress. When the stress was beyond the limit of elasticity of the material the result was strain or permanent deformation. The resistance a material was able to oppose to an external force depended on the manner in which the load was applied. He entered into an interesting history of the growth of knowledge with regard to formulas for beams and girders, and by the use of models, diagrams, etc., showed how the reactions and bending movements in beams were determined. Tho first bridges built by man were, he said, probably a close imitation of Nature. . Most probably the first was a log that had got thrown over a stream, and the first actually made by man would be similar. The Gothic arch, the strongest of all arches, was a pure imitation of those rock bridges to bo found in mountainous country and on the seashore. In the mountains such natural bridges in course of time scaled away under the influence of weather till they assumed the perfect Gothic form, when scaling ceased, leaving the permanent result. Driftwood and large tree trunks heaped over wide streams in flood time would soon show the way to make permanent structures overrivers. Strange to say, there was no mention of any bridge in the Bible, closely identified though tho Jews were with Egypt and the Roman world. The Romans were great bridge builders. The first bridge mentioned in any historical record occurred in the quaint Chaldean narrative of the Fall. This narrative approximated closely to the Bible version, but, as he had said, tho Bible did not mention bridges. After leaving the Garden of Eden, Adam and Eve wore penned up by thunder, lightning, and ram on a tongue of land at the junction of the Euphrates and Tigris, and Adam “ gathered a' huge trunk, threw it across the stream, and passed over into the land of Ur. The rest of the lecture was of a highly technical character, dealing with the method of arriving at the actual stress imposed upon the various beams and stmts of bridges, and like theoretical problems.