690 



NATURE 



{Oct, 31, 1878 



in the manner which was formerly adopted by Mr. Airy 

 in the mounting of the equatorials at Cambridge and 

 Liverpool. With the inauguration of the new equatorial 

 in the year 1859 ^^ change from the old state of the 

 Observatory was complete. There was not then a single 

 person or instrument in the Observatory that had been 

 there in Mr. Pond' s time. 



A fifth new instrument was planned by Mr. Airy in the 

 year 1869, and erected in the following year in the Royal 

 Observatory, in order to decide the most delicate question 

 of the dependence of the measurable amount of sidereal 

 aberration upon the thickness of the glass or other trans- 

 parent material in the telescope. The tube of a telescope 

 (the lenses of which were ground to proper curves) was 

 filled with water, and the telescope mounted as zenith- 

 sector. Several years' observations of y Draconis did 

 not reveal a perceptible difference in the constant of 

 aberration found in this manner from the value generally 

 adopted. 



Of the instruments invented by Sir George Airy I may 

 mention also the double-image micrometer, a very useful 

 apparatus, if thoroughly investigated ; the eye-piece for 

 correcting the atmospheric dispersion ; the orbit-sweeper, 

 a most ingenious contrivance to detect comets approaching 

 perihelion passage, the time of which cannot be exactly 

 fixed. 



The observations were made, under his own responsi- 

 bility, during nearly half a century, without interruption, 

 reduced with great care, regularly printed, and — a very 

 essential thing — very liberally distributed. They form a 

 vast collection of the most important fundamenta of 

 astronomy. Every year Sir George publishes a report 

 on the work done in the Royal Observatory ; these re- 

 ports form a series which will be of the greatest use for 

 the writer of the history of astronomy and science in 

 general in the nineteenth century. 



Since the year 1833 the incessant activity of Sir George 

 Airy had been directed to an undertaking, proposed to as- 

 tronomers by Bessel, in the preface of his " Tabula? Regio- 

 montanse," viz., the reduction of the Greenwich lunar and 

 planetary observations since 1750. This most arduous task 

 was completed in the year 1 848 ; and we may say that our 

 present tables of the motions of the moon and the planets 

 rest, for the greatest part, on those bulky volumes, con- 

 taining these reductions. 



But not only was this immense magazine of dormant 

 facts opened by Sir George to science : he reduced also 

 the observations of Groombridge, of Catton, and of Fal- 

 lows, the first Astronomer- Royal of the Cape of Good 

 Hope. The importance of these reductions is not limited 

 by the usefulness of the observations themselves to the 

 astronomer by the appearance of the " Star-Catalogue," 

 containing Mr. Groombridge's most valuable observations. 

 Mr. Johnson, for instance, was induced to undertake 

 those beautiful observations of circumpolar stars, form- 

 ing afterwards the Radcliffe catalogue of stars. Prof. 

 Hansen, of Gotha, was very materially supported by the 

 Astronomer- Royal in finishing his great work on the 

 moon and calculating tables of her motion. 



The pressure of daily work and the responsibility of 

 keeping up the Greenwich series of solar and lunar 

 observations absolutely uninterrupted, did not prevent 

 the Astronomer-Royal from taking up other scientific 



questions of the day. In the year 1842 he made a voyage 

 to Turin, in order to observe the total solar eclipse ; the 

 same object induced him to visit Gothenburg, in Sweden, 

 in 1 85 1, and to organise, in the year i860, the famous 

 Himalaya expedition to Spain. 



His great interest in every branch of his favourite 

 science is evinced by the recent introduction at Green- 

 wich of heliographic and spectroscopic services. 



In the year 1847 Sir George went to Russia for the purpose 

 of inspecting the new Russian Central observatory. It is 

 highly gratifying to read with what absence of prejudice 

 the great astronomer expresses himself in regard to this 

 observatory, the personal establishment of which and the 

 construction of instruments is so very different from those 

 at Greenwich. 



Magnetical and meteorological observations were not 

 made at Greenwich before the time of the present Astro- 

 nomer-Royal. Sir George Airy proposed to the Govern- 

 ment to make them at Greenwich, and since 1 838 the 

 new Magnetical and Meteorological Observatory has 

 been in activity. He introduced for this department 

 also the self-registering instruments constructed by Mr. 

 Brooke. 



In later years the Astronomer-Royal has been op- 

 pressed with the difficulty of making the meteorological 

 observations practically available. With a store of re- 

 cords, extensive, accurate, and rich, beyond any other 

 which exists, he does not see a probability of physical 

 connections or physical laws sufficiently strong to induce 

 him to enter confidently on an expensive comparison, and 

 he expresses strongly his opinion, that the want of 

 meteorology at the present time is principally in sugges- 

 tive theory. 



Only very briefly can I mention his very useful experi- 

 ments on iron-built ships, for the purpose of discovering 

 a correction for the deviation of the compass, which 

 resulted in a system of mechanical corrections, univer- 

 sally adopted ; his researches on the density of the earth 

 by observations in the Harton Colliery ; his extensive aid 

 to Government in recovering the lost standard for mea- 

 sures ; in fixing the breadth of railways ; in introducing a 

 new system for the sale of gas, &c. All these transac- 

 tions have proved Sir George Airy "the thorough man 

 of business." Indeed, the promptness of his corre- 

 spondence and his kindness in answering every scien- 

 tific inquiry in the most minute manner, is most re- 

 markable and seldom to be met with in so profound a 

 philosopher. 



In recent years the Government intrusted to his care 

 the equipment and instruction of the British Expedition 

 for the Transit of Venus, a subject which had engaged 

 the attention of the Astronomer- Royal during thirty years, 

 and had induced him to write a number of most im- 

 portant papers on the matter. In the year 1848 he 

 gave a series of lectures on this difficult subject at 

 Ipswich. The whole responsibility for reducing the ob- 

 servations made during the transit rests likewise with 

 him. Much of his time has, during the last few years, 

 also been spent in promoting the lunar theory by a 

 method of his own. 



Sir George Airy has, of course, deservedly received 

 the recognition of his country and the scientific world 

 in general. He is medallist of the French Institute, 



