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Many of the bearings are situated in dark places, and cannot be seen. There are others that are difficult of access as in the case of bearings of screw-propeller shafts. Serious mischief may result before the heating of the bearing proclaims its dangerous condition. In some cases the timber work is set on fire, which may result in serious consequences.
So far as the screw-propeller was thought of as a means of propulsion, it lay under a suspicion of loss of efficiency due to the oblique nature of its action, and this was supposed to be such as to render it necessarily and essentially less efficient than the paddle-wheel.
The close of a hot day on board Her Majesty's ship "Startler," whose engines kept up a regular pulsation as the screw-propeller churned the water astern into golden and orange foam.
At the same time it must be admitted that the screw-propeller as a possibility for marine propulsion was known in a vague way to the engineering practice of the day, and it is at this time of course quite impossible to say how much may have been known by Ericsson, Smith, or others concerned in later developments, or to what extent they may have been dependent for suggestion on what had preceded them.
In the Strait of Gibraltar he explained to him the great currents sent by the ocean into the Mediterranean, at certain times aiding the screw-propeller in the propulsion of the vessel. Without this Atlantic current the mare nostrum, which lost through atmospheric evaporation much more water than the rains and rivers could bring to it, would become dry in a few centuries.
"Somehow I got upon my feet, or dreamed I did God knows where dreaming ended and reality began. Gentlemen maybe you'll conclude I went mad last night, but as I stood holding on to the bedrail I heard the blood throbbing through my arteries with a noise like a screw-propeller. I started laughing.
They came up against the problem to which Riach has since devoted so much attention, that of propeller design. 'We had thought of getting the theory of the screw-propeller from the marine engineers, and then, by applying our table of air-pressures to their formulae, of designing air-propellers suitable for our uses.
The most important points of contact between Ericsson's work and these advances were in connection with his introduction of the surface condenser, the use of artificial draft, devices for heating feed water, his studies in superheated steam and its use, and his work in connection with the development of the compound principle in steam-engines, his relation to the introduction of the screw-propeller, and to the use of twin screws at a later time.
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