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THE POPULAR SCIENCE MONTHLY.

of vision. The current years have been rich in results in the regular work of the institution, as the published volumes of observations bear testimony. A new observing room for the transit-circle was erected in the west wing, and the mounting of the circle was completed in 1870. The library was removed to the room previously occupied by it, and now numbers more than 5,000 bound volumes. The total solar eclipses of August 7, 1869, in America, and December 22, 1870, in Europe, were closely observed by parties from the observatory, and full reports of their observations were published.

But the greatest achievement toward raising the observatory to a higher rank among its peers was the successful completion and mounting, in the new tower and dome prepared for it, of the Great Equatorial, in the month of October of the past year. This auspicious event is largely owing to the persevering effort of the superintendent. After repeated representations concerning the necessity of the instrument, Congress made an appropriation of $50,000 for the purpose. The contract was made in August, 1870, with Messrs. Alvan Clark & Sons, of Cambridgeport, Mass. They agreed to construct a refracting telescope, of good definition, and of 26 inches clear aperture, mounted equatorially on the German plan, and supplied with all the appliances that modern science has developed. They required four years to complete it. But the opticians were ahead of their contract, and the observatory is now rejoicing in the absolute possession of the talismanic instrument which has been the object of its ambition.

The future work of the institution will demand all its resources. It is already in the full tide of preparation for the observation of the coming transit of Venus in 1874, for which it has received an appropriation of $150,000. It is looking forward to still more satisfactory results from the transit of 1882, which will be specially favorable for observation on American ground, while an opposition of Mars, in 1877, will test the power of its new possession.

With this grand telescope and its equipment, with a personnel made up of officers who honor their profession, with Congress ready to grant all needful aid, there is every reason to anticipate a future for the United States Naval Observatory, honorable to itself, and honorable to the country it represents.

 

THE MANTIS, OR PRAYING INSECT.

SPECIES of insects known as Mantids belong to the order Orthoptera, which includes crickets, grasshoppers, cockroaches, locusts, etc. The following figure illustrates the appearance of one of these. They are of bright, variegated colors, and are sometimes quite large, even three or four inches in length. The mantis lays its eggs at the