< Page:Popular Science Monthly Volume 6.djvu
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EDITOR'S TABLE.

thetic cooperation. When the different races and nations come into relation in the sphere of politics or religion, antagonisms, discords, jealousies, and hate, are almost inevitably engendered. But, when these are put aside, or kept out of view, and the object to be attained is simply to extend the knowledge of Nature, the better elements of humanity begin to be recognized and asserted. As a striking illustration of this, we have the curious fact that, with reference to the approaching eclipse, it is not the Europeans, but the "King of Siam who has taken the initiative in inviting astronomers to his dominions, and providing for their entertainment while there." On the 9th of last October, his Siamese majesty, through his private secretary, Bhashakarawangse, extended this courtesy to the Royal Astronomical and Royal Societies, and to any astronomers they might accredit to him for the purpose of utilizing the coming opportunity. The English Government sends out an expedition; and an expedition by the French Government goes under the control of M. Janssen. Dr. Hermann Vogel, the eminent Berlin astronomer and photographer, will join the expedition of Janssen at Singapore, and Prof. Tachani will represent the Italian observers.

An intelligent writer in the Herald, in the full account which he gives of the preparations for the coming eclipse, thus describes an instrument which has been recently constructed to facilitate observation, and from the use of which much aid is to be expected:

"The siderostat was devised to enable the observer to escape the inconvenience and often the impossibility of changing his position to follow the eye-piece of his telescope, when turned upon the moving sun or star. With the best telescopic mountings and arrangements which have heretofore been employed, the observer is put frequently in the most uncomfortable positions, and his work subjected to those errors irreparable from the nervous handling of his glasses at the exciting and critical moment of the eclipse. The ingenious scientist, Foucault, the perfecter of the siderostat, aimed to give the equatorial the power of making the entire heavens pass before the observer without his having to disturb himself or to displace the instrument. The siderostat, as arranged by him, is, therefore, a telescope fixed horizontally in an invariable position, before which a plane mirror brings successively the various points of the sky. The whole rests on a brass stand, supported by three screws, with two levels and a regulating azimuth movement. The plane mirror is carried by an horizontal axis on the top of two vertical supports, which revolve round a centre, the movement being perfectly effected by small wheels at the foot of the supports. By the employment of the isochronous regulator of Foucault, placed at the foot of the instrument, a motion sensibly equal to the diurnal motion is communicated to the plane mirror, so that the heavenly bodies maintain invariable positions in the field of the horizontal telescope, in front of the apparatus directed toward the mirror. This clock-movement, which has been applied to equatorials, is perfectly regular, and won for its inventor the grand prize in the mechanical arts at the Universal Exhibition of 1867. The apparatus gives perfect steadiness in experiments for measuring the position of spectrum lines and of the displacement of the lines by means of large fixed spectroscopes. Its adaptability has been tested during the recent photographic experiments in connection with the transit of Venus, and with the greatest ease it combines with the observing telescope the apparatus necessary for the work of celestial photography for photometric researches. The complete instrument, telescope and siderostat, placed in the plane of the meridian, may also be regarded as a meridian instrument, so that it is, perhaps, the most powerful weapon of modern astronomy; and, when desired, spectroscopes and photographic apparatus can be attached to the eye-piece of the telescope, of a size even larger than the telescope itself."

THE LITERATURE OF EVOLUTION.

A correspondent applied to the editor of the Nation asking "for information on books relating to the development or evolution theory, especially for the book 'which is not too partisan or too technical, but gives the facts and reasonings with reference to it on both

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