THREE:It is exceedingly difficult for an apprentice engineer, without experimental knowledge, to choose plans for his own education, or to determine the best way of pursuing such plans when they have been chosen; and there is nothing that consumes so much time, or is more useless than attempting to make original designs, if there is not some systematic method followed.
THREE:The puzzled and slightly dissatisfied audience poured out of the inquest hall with a feeling that they had been defrauded. There was no chance of a verdict of murder against Bruce after the last two bits of startling and quite unexpected evidence. Two credible witnesses had proved that one of the people who had called Bruce to the corner house had remained after he had left. The case was just as fascinating, and at the same time as puzzling as ever. The real culprit as yet might have to be found, but there was no getting away from these facts about the stolen banknotes. Still, the coroner's jury were not called to try that question, and at the suggestion of Prout the matter was adjourned for a month.Chewing gum? Jeff was startled. Swiftly he strode across the dimly sunlit floor, got onto the forward step, peered into the cockpit.
THREE:The poor man wept, and, although I had taken with me no more than two pieces of bread-and-butter, which I had not touched yet, I could not bear the sight of these poor, hungry things, and handed over to them my food.
THREE:The officer shook his head in a puzzled kind of way. He knew nothing about any woman. Perhaps those below had accounted for her. There were lights all over the house when Lalage was led down with the handcuffs on his wrists.
THREE:"I must see further into this," Hetty told herself. "When this honoured guest comes I will creep downstairs and listen. It's not a very nice thing to do, but if ever the end justifies the means, surely this is a case in point."
THREE:Movements and strains may be called two of the leading conditions upon which designs for machines are based: movements determine general dimensions, and strains determine the proportions and sizes of particular parts. Movement and strain together determine the nature and area of bearings or bearing surfaces.
THREE:Different kinds of gearing can be seen in almost every engineering establishment, and in view of the amount of scientific information available, it will only be necessary to point out some of the conditions that govern the use and operation of the different kinds of wheels. The durability of gearing, aside from breaking, is dependent upon pressure and the amount of rubbing action that takes place between the teeth when in contact. Spur wheels, or bevel wheels, when the pitch is accurate and the teeth of the proper form, if kept clean and lubricated, wear but little, because the contact between the teeth is that of rolling instead of sliding. In many cases, one wheel of a pair is filled with wooden cogs; in this arrangement there are four objects, to avoid noise, to attain a degree of elasticity in the teeth, to retain lubricants by absorption in the wood, and to secure by wear a better configuration of the teeth than is usually attained in casting, or even in cutting teeth.
THREE:Tangent wheels and spiral gearing have only what is termed line contact between the bearing surfaces, and as the action between these surfaces is a sliding one, such wheels are subject to rapid wear, and are incapable of sustaining much pressure, or transmitting a great amount of power, except the surfaces be hard and lubrication constant. In machinery the use of tangent wheels is mainly to secure a rapid change of speed, usually to diminish motion and increase force.