twenty miles per second. That there has been some remarkable change 

 in the movement of this star in respect to the solar system we may well 

 believe when we read Humboldt's statement, that observers who noted its 

 appearance two thousand years ago describe it as a bright red star. Its 

 rate of departure must have very much diminished during that time in 

 order to shorten the wave-lengths sufficiently to change its color from a 

 bright red to a light yellow. 



Science has reached a stage wherein its own progress, reacting from the 

 effect of mechanical inventions which it occasions, is very materially accel- 

 erated. To say nothing of such instruments as the spectroscope and the 

 transit instruments, the improvements in the manufacture of object glasses 

 for achromatic telescopes have rendered possible unhoped for achieve- 

 ments. One of the most skilful manufacturers of telescopes now living — 

 our own countryman, Clark — has undertaken the construction of a refractor 

 for the United States Observatory which will have a clear aperture of 26 

 inches ! It should have double the power of the celebrated instrument at 

 Cambridge which has done such eminent service, its defining power being 

 superior to the great reflector of Lord Rosse. 



But perhaps the most wonderful instruments invented to supplement our 

 imperfect senses are those employed to render visible the contour of the 

 electric sparkor the lightning flash. Professor Rood's contrivance for this 

 purpose is an ingenious combination of Becquerel's phosphoroscope with 

 Wheatstone's photometer. By it he can measure the duration not only of 

 the entire flash of electric light, but can follow it through its several stages, 

 and measure each one even down to the ten billionth part of a second. He 

 finds that the duration of the brightest electric sparks is but one twenty-rive 

 millionth of a second each. The singular property of phosphorescence, or 

 the retention of light after exposure to it by such bodies as phosphorus, the 

 diamond, and some others, is discerned by Becquerel's instrument to belong 

 in a less degree to all bodies. A "seismograph" is an instrument for the 

 automatic registration of earthquake shocks. Whenever the shock comes, 

 it records all of its phases by means of a very delicate and complicated 

 machine. Its direction, its intensity, whether vertical or horizontal, the 

 number of shocks, the time of their occurrence and their duration, all are 

 recorded. This apparatus is used in the Observatory of Mount Vesuvius. 

 A similar device has been applied to register the history of the waves of the 

 sea, and also for detecting and measuring atmospheric electricity. 



The spectroscopic experiments on the Nebula; have proved them, at least 

 in some instances, to be of a gaseous instead of a solar nature. More won- 

 derful has been the revelation regarding the nature of comets and meteoric 

 showers. Schiaparelli identified one of the comets of 1862 with the August 

 meteor shower. It requires six hours for the earth to traverse the cometary 

 ring that intersects the earth's orbit at the point which it passes on the 

 10th of August. Further calculations have identified the comet of 1866 

 with the November shower of meteors, which has at times presented 

 the startling phenomenon of a rain of falling stars. Thus the former terror 



