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THE POPULAR SCIENCE MONTHLY.

wood grows on this island. The instruments must next be mounted, and all gotten in readiness for work.

The astronomer and his assistant set up the transit, the small equatorial (five inches' aperture, and about seven feet long), and the clock, and provide safe places for their chronograph and chronometers. Suppose a chronometer-spring breaks now: there is no help nearer than New York. The two photographers put up their hut and prepare for work. From this time until the time of the transit, all is work.

Every day the methods which will be adopted on the important day are rehearsed. Each one does the very thing which he will do, takes the very steps which he must then take, and turns the very same micrometer-screws just as he will turn them in December. This is repeated until every one is sick of it, and, from a man, each becomes a machine.

During the nights the chief astronomer is looking for occultations, or taking differential measures between the moon's limb and a star, while the assistant is determining time and latitude. Sometimes their work is interchanged, to eliminate any personal peculiarities of observing. When the final day comes, they should have their latitude and longitude thoroughly well known, and their clocks and chronometers rated perfectly. The photographers, too, should know the exact strength of both, the precise time of exposure, and the right developer to make the best possible negative of the sun.

When the time of transit actually comes, the chief will be at the equatorial, and will observe the first contact, and record the time on his chronograph, and at once commence measures of the distance of cusps. The assistant astronomer will see that the heliostat which is to throw the image of the sun into the stationary photographic telescope does this properly; and within the dark room the two photographers must be taking negatives as rapidly as possible.

This continues during the transit from first to second contacts; afterward the photographs succeed each other, but not so rapidly, and finally, the last contact is marked. It is all over now, and there is nothing to do but to write down at once all notes which are to be used in the report, and to prepare for a journey home.

Six or eight months on a rocky island, vast expense, and much trouble and discomfort: but le jeu vaut la chandelle. The moral of it is, that Science expects every man to do his duty. Let us hope that Science will not be disappointed.