The expected return of Halley’s comet in 1835 again stimulated popular interest in the science, and aroused an intense desire to provide serviceable instruments, and to establish buildings suitable for their care and use. To Williams College, Massachusetts, belongs the honor of erecting, in 1836, the first astronomical observatory on this continent. Under its revolving dome was mounted an Herschelian telescope of ten feet focus, which later became the property of Lafayette College, where it is still preserved. In 1843, John Quincy Adams laid the corner-stone of the Longworth Observatory in Cincinnati, and delivered a commemorative address, his last great oration. The construction of the United States Naval Observatory at Washington soon followed, and before 1850 there were fourteen observatories established in this country. Nearly all the instruments they contained were made abroad, chiefly in Munich and London. Since then the number has risen to two hundred recognized observatories, of which twenty-four are of superior order, where systematic work is daily pursued, and the results are regularly published in book form. About two hundred observatories exist in other nations. VII. IMPROVED INSTRUMENTS; THEIR EFFECT ON THE SCIENCE. The great improvements in telescopes made during the century have been fruitful in two ways; a better knowledge of the surface of the moon and of the planets has been gained, and we have been enabled to learn with precision the exact motions and times of revolution of these bodies and of their accompanying moons. This information, by the use of the laws ascertained by Kepler and La Place, gives us their exact distance, dimensions, and mass. With the increase of telescopic power, the census of the starry host has been so augmented that the number of stars within reach of our modern instruments exceeds 125,000,000. But we had gone little beyond this sort of information until the invention of the spectroscope. Previous to the year 1859 a few meteors, composed chiefly of stone or iron, some of which had been actually seen to fall from the sky, had been subjected to chemical analysis; but outside of this naught was known of the physical constitution of other worlds than ours. Our ignorance on this point was complete. All our attempts to become better acquainted with the structure of the planets, the composition of the sun, and the nature of the fixed stars would probably have been in vain but for the invention of the spectroscope. This surprising instrument is a master-key with which to unlock many of Nature’s mysteries; her recesses are brought to view, and the farthest star is subjected to an accurate chemical analysis, so far as the light that comes from it is sufficient to disclose the materials of which it is composed. [Illustration: THE LICK OBSERVATORY, MOUNT HAMILTON, CALIFORNIA.]