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THE COMING TRANSIT OF VENUS.

lege Observatory and Greenwich some years ago, and it is now known that the result obtained was greatly in error. Indeed, Prof. Peirce, in his discussion of the series of observations, came to the conclusion that it was impossible to derive the longitude of a place by this means, certainly, within one second of time.

The Americans and Russians intend to depend on the occultations of small stars by the moon.

Occultations are much more likely to be free from systematic errors than the moon-culminations, and, if they can be observed throughout a lunation, a compensation of errors will obtain.

The Russians intend to mask their stations of observation, and subsequently to connect by telegraph St. Petersburg with the most important of them. The transportation of chronometers to and fro between the stations whose longitude is thus determined and the minor ones will assure the longitude of the latter.

The American parties in the southern seas will be transported to their various stations in a ship-of-war which will touch at the different islands and leave the parties, and which will make chronometric expeditions between the various stations. Besides this, all existing telegraph-lines will be utilized. As each of the parties of each nation is to be led by some astronomer of eminence, it is certain that no means will be neglected to make the preliminary results of the greatest attainable accuracy.

The various assistants are now in training at Greenwich, Poltava, and Washington, with the very instruments which they will use on the expeditions.

At Washington and Poltava an apparatus for the representation of the transit is in use. A disk representing Venus is caused to travel over an illuminated space which is representative of the sun, and the circumstances of the transit are then observed.

In this way it is hoped to obtain an idea of the personal error of each observer in watching contacts, so that, in reducing the observations of the transit, all personality may be eliminated.

Most of the American parties will start in the spring of 1874, and proceed in the most expeditious way to their stations. They must take with them every thing which they can need during their stay, for in most of the stations there is no supply of any kind to draw upon.

We can hardly realize the absolute necessity of being provided with every thing that may be needed on such an expedition: but let us conceive the feelings of an astronomer on a desert island with no screw-driver, or with no ink, or matches, or soap!

There is no repairing a blunder of outfitting in these cases, and the greatest care has to be exercised in providing for all contingencies.

Arrived at its station the party will put up its observatory, a little wooden or canvas hut which has been brought from America, for no