Page:Popular Science Monthly Volume 4.djvu/224

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planning of machinery, so that it shall be at once economical and durable in operation, and simple and cheap in construction, is not merely an important incidental duty, it is absolutely the chief and most difficult duty of the mechanical engineer.



THE nature of a transit of one of the inferior planets (Mercury or Venus) is well understood, and the phenomena attending such a transit have been thoroughly discussed, and fully described in many places. The importance of the observation of these transits, and the general character of the results expected from the expeditions sent out to observe them, are probably understood by all, but it is thought that a brief account of the means that are to be employed to accomplish the desired end will be of interest.

The records of the plans which have been formed, and of the preparations which have been made by the different governments of the world and by private individuals, are, unfortunately for the general public, published only in proceedings of scientific societies, or in many cases they exist only in manuscript. When the expeditions return home after the observations are made, in astronomical Europe and America will resound the busy hum of preparation, and from the beginning of 1875 the reader of astronomical items will be sated.

At first will come a series of preliminary reports as the parties come in; then we shall have the final reports, giving numbers, data, descriptions of instruments, and the observations made at the transit, the longitudes and latitudes of the various stations, and, in short, every result which the practical astronomer will have derived.

These final reports will be eagerly looked forward to, for upon them depends the constant of solar parallax, and from them will be deduced the definitive result of all the astronomical work done on the globe on that day.

We know already that the final outcome of all these vast preparations which we are going to describe will be a number very near to 8“.848.

The whole world is united in an effort to know exactly how to change this; whether to write it greater or less. But the results of these expeditions, if they are successful (and we can hardly fail of success), will be, not simply the establishing of the earth's distance from the sun on a certain basis, but much more.

So many expeditions of trained scientific observers will bring back with them data only second in importance to the main object of their