440 HISTORY OF SCIENCE. 



in latitude 41, thirty-five hours; in latitude 19, seventy-one hours; 

 in latitude 5, eleven days would be the times approximately. The 

 experiment is usually performed by suspending an iron ball of at least 

 14 Ibs. weight by a very fine and long steel wire. The length of the 

 suspending wire should be at least 20 feet, though with even a height 

 of 1 2 feet the effect is observable. The experiment has occasionally 

 been very well exhibited in very lofty buildings, such as churches. 

 Fig. 196, from the roof of which a very long wire could be suspended. 

 The change in the direction of the plane of oscillation in the space of 

 an hour can be seen by a large audience, and its rate may be followed 

 by means of a graduated horizontal circle. It will of course be under- 

 stood that a properly suspended pendulum of this kind will continue 

 its oscillations for several hours. 



The progress of astronomy is indicated by the great increase in the 

 number of observatories. At the opening of the present century many 

 national observatories had been established. Englishmen have occa- 

 sion to regard with satisfaction the work done at the Royal Observatory 

 of Greenwich, for the observations made there have been conducted 

 with the utmost regularity, and their correctness has never admitted 

 of a doubt. It is from the materials furnished by these excellent ob- 

 servations that astronomers have succeeded in bringing their tables 

 of the sun, moon, and planets to the present state of perfection. For 

 the complete knowledge of the moon's motions especially, the world is 

 indebted to the Greenwich establishment ; and mainly to data derived 

 from observations made here are due the precise determinations of 

 aberration (p. 250), refractions, etc., which we now possess. Delambre 

 remarks in his " History of Astronomy in the Eighteenth Century," 

 that were all other records of the science destroyed, the Greenwich, 

 observations alone would furnish materials sufficient to reconstruct 

 the whole body of astronomy. In more recent times our national 

 observatory enlarged its scope by the addition of appliances for the 

 study of meteorological and magnetical phenomena, and the records 

 kept in these departments have been published with the same regularity 

 as the astronomical observations. The value of these observations, 

 so trustworthy, regular, and prolonged, has been incalculable. 



Among the most notable of the observatories erected during the 

 present century may be mentioned the new one established by the 

 Russian Government in 1839 at Pulkowa, a small town about ten miles 

 from St. Petersburg. This establishment has been designed on a 

 magnificent scale, and provided with the finest instruments from the 

 hands of the best German and English artists, and altogether it may 

 be considered as one of the most complete observatories in the world 

 The cost of its erection and equipment amounted to ^1 00,000, ana 

 more than ;i 0,000 per annum are supplied by the imperial treasury 

 for its maintenance. 



In the United States astronomical pursuits have been encouraged 



