11 



work. The subjects also were of the most varied kinds and on all 

 parts of mathematical philosophy. At first he wrote chiefly for the 

 Cambridge Philosophical Society ; thus in March, 1824, he calculates 

 the effect which the ring of Saturn produces on his figure. He tries 

 to verify the curious observations of Herschel that this planet is pro- 

 tuberant between the poles and the equator, but he finds that theory 

 leads to an exactly opposite result. The observations of Herschel 

 were, however, considerably modified by those of Bessel some years 

 after. In another paper in the same year he discusses achromatic 

 eye-pieces ; for this and his other papers on optical subjects, the Copley 

 Medal of the Royal Society was adjudged to him in 1831. Soon after, 

 he writes on the proper forms of the teeth of wheels, though, owing 

 to the extensive use of iron where wood was formerly used, this 

 subject has no longer the interest it once had. 



One of the most interesting papers written by him, about the year 

 1825, is on a peculiar defect of his own eye and the mode of correcting 

 it. He discovered that in reading he did not use his left eye. Sup- 

 posing this to be due to habit, he endeavoured to read with the right 

 eye shaded, but found he could not distinguish a letter at whatever dis- 

 tance from the eye the characters were placed. Some time after he 

 made a further discovery, viz., that the image of a point formed by that 

 eye was not circular but elliptical. From this and other appearances 

 he inferred that the refraction of the eye was greater in the vertical 

 plane than in that at right angles. To correct this it would be 

 necessary to use a lens which would refract more powerfully the rays 

 in one plane than those in the perpendicular plane. His idea was 

 that the lens should have one surface cylindrical and the other 

 spherical, and he describes at length his experiments to determine 

 the proper radii. The result was so successful that he was able to 

 read the smallest print at a considerable distance with the left eye 

 as well as with the right. In his subsequent papers he frequently 

 returns to this subject and makes several reports to the Society on 

 the changes produced in his eye by lapse of time. 



In 1826, when Ivory criticised Laplace, Mr. Airy, in a paper contri- 

 buted to the Cambridge Philosophical Society, was not afraid to in- 

 tervene between two such distinguished analysts wlien he thought that 

 both had gone wrong. Mr. Airy was not indisposed to controversy ; 

 possibly it added a touch of life to his science. We find him after- 

 wards engaged in many disputes, in all of which he was able to prove 

 that he was a tough adversary. In this year, three years after his 

 degree and ten years before he became F.R.S., he read his first paper 

 before the Royal Society. The subject was the much debated question 

 of the figure of the Earth. Alluding in it to the peculiar views of 

 Ivory of fluid equilibrium, he was attacked by that mathematician 

 in a somewhat arrogant manner. This called forth from Mr. Airy a 



