SKETCH OF SIR G. B. AIRY. 103 



where to be found is the one he there constructed in 1860, the circles 

 being no less than six feet in diameter, and the telescope affixed be- 

 tween the two graduated disks being twelve feet long, and having an 

 object-glass of as many as eight inches in aperture. Through this 

 splendid apparatus the altitude of the stars, as well as the time of 

 meridian passage, is now unerringly marked at the great national ob- 

 servatory. But the greatest of all the instruments established by him 

 at Greenwich is a large, first-class equatorium, well known among 

 astronomers. 



During Sir George Airy's rule at the observatory he has, in the 

 midst of his other labors, reduced the Greenwich observations of the 

 moon and of the planets from 1750 down to the present tfme. Inci- 

 dentally he has thrown considerable light on ancient chronology by 

 his ingenious calculation of some of the most renowned of historical 

 eclipses. Thrice the Astronomer Royal has taken occasion to visit the 

 European Continent for the purpose of making more accurate observa- 

 tions upon the solar eclipse then eagerly anticipated. In 1854 he ap- 

 proximated more nearly than any previous investigation had done to 

 the weight of the earth, through a series of experiments on the relative 

 vibration of a pendulum at the top and bottom of Harton Coal-pit. 



Sir George Airy has been repeatedly called into council on matters 

 of grave difficulty by the government. He was chairman of the royal 

 commission empowered to supervise the delicate process of contriving 

 new standards of length and of weight, the old standards having been 

 destroyed in 1834 in the conflagration of the Houses of Parliament. 

 He was consulted some years afterward by the government in respect 

 to the bewildering disturbance of the magnetic compass in iron-built 

 ships-of-war. Thereupon he contrived an ingenious system of mechan- 

 ical construction, through a combination of magnets and iron. The 

 result was successful, and the system generally adopted. He conducted 

 the astronomical observations necessary to the drawing of the boun- 

 dary-line now traceable on the map of the New World between the 

 Canadas and the United States. During the battle of the gauges in 

 the railway world Sir George Airy strenuously advocated the narrow 

 gauge, and he just as energetically advocates the adoption of a decimal 

 currency. The writings of the Astronomer Royal are numerous. He 

 has contributed largely to the Cambridge Transactions and the Philo- 

 sophical Transactions. His pen has notably illustrated the memoirs 

 of the Astronomical Society. He has written abundantly for the 

 Philosophical Magazine, and still more abundantly, under his reversed 

 initials, A. B. G., in the columns of the Athenceum. His principal 

 works, however, are those which may be here rapidly enumerated : 

 " Gravitation," published in 1837, was written originally for the " Penny 

 Cyclopaedia." " Mathematical Tracts" have reached a fourth edition, 

 as have also his " Ipswich Lectures on Astronomy." In 18G1 appeared 

 his treatise on "Errors of Observation;" in 1869 his treatise on 



