Page:Popular Science Monthly Volume 12.djvu/160

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come completely filled and their valves closed, and then sets it in motion on the return-stroke. Thus the pistons move alternately. These engines have given a very high duty. The condenser is seen at C, and the air-pump is at D, the latter being worked from the bell-crank lever H by means of links, I, K. The steam-valves, Q, R, are balanced. V V are the water-induction valves, and T T those on the eduction-side.

Here we leave the steam-engine as applied to raising water. We have invariably noticed, in the forms of engines so used, that a condenser forms a part of the apparatus.

We will next briefly trace the history of that now familiar form of engine in which the steam, having done its work, is discharged directly into the atmosphere.



A REMARKABLE discovery has been made by the astronomers of Lord Lindsay's observatory at Dunecht—a discovery the true meaning of which is not as yet fully perceived. It may be remembered that some nine months ago a new star, as it was called, made its appearance in the constellation Cygnus[1]. This object shone out where before no star had been known to astronomers—not merely, be it noticed, where there was no visible star, but where none was recorded even in lists like Argelander's "Durchmusterung," containing hundreds of thousands of telescopic stars. It was not, however, altogether impossible that some small star within moderate telescopic range had existed in the spot where the new star shone out, and that in some way this small star had escaped observation. This seemed the more likely because the new star had appeared in a part of the heavens very rich indeed in telescopic stars; at any rate, astronomers had reason to believe that they would be readily able to determine the question with a high degree of probability by watching the star as it gradually faded out of view. For a "new star" which had shone out in the constellation of the Northern Crown in May, 1866, and had been identified with a tenth-magnitude star in Argelander's list, had gradually faded out of view, and, growing yet fainter, had sunk through one telescopic magnitude after another until it shone again as a tenth-magnitude star only. Since that star had resumed its former lustre, or rather its former faintness, it seemed not unreasonable to conclude that so also would the star in Cygnus. We shall presently see how far this expectation was from being fulfilled.

  1. See Popular Science Monthly, vol. xi., p. 59.