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CHAPTER XXVII. COMPOUND HAMMERS.The driver was clad in goggles and leather coat, thereby proclaiming the fact that he was used to a high rate of speed. He placed a note in Bruce's hand; there was an interrogative gleam in his eyes.
Bruce nodded. He was beginning to have some feeling of hope.He was gone at last; the hall door closed behind him. His footsteps echoed on the pavement a few yards and then stopped. After that the whole world seemed to be wrapped in silence. It was nearly dawn before Leona Lalage crept into bed. She carefully locked away some papers that she had almost committed to heart. There was triumph in her sleepy eyes.
Drilling differs in principle from almost every other operation in metal cutting. The tools, instead of being held and directed by guides or spindles, are supported mainly by the bearing of the cutting edges against the material.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.
"Not at all," said the Doctor, endeavouring without much success to treat his guest as an ordinary being, "I am to blame. I ought to have realised that you would require nourishment. But, of course, I am still in the dark"
Still I frowned. "How does it come that she's here, anyhow?"