7io 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 mount- 

 ing, in the new tower and dome prepared for it, of the Great Equa- 

 torial, 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 instru- 

 ment, 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 com- 

 plete it. But the opticians were ahead of their contract, and the ob- 

 servatory 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 appro- 

 priation 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 hon- 

 orable to the country it represents. 



+«+ 



THE MANTIS, OE PRAYING INSECT. 



SPECIES of insects known as Mantids belong to the order Qrthop- 

 tera, 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 



