from the different astronomical observatories of the country. The observations were successful; they gave the result that gravity is increased at the depth of 1260 feet by 1/19000th part: from which he estimated the density of the Earth to be 6.565. Airy not only supplied Hansen with the Greenwich observations of the Moon for the purpose of constructing his Lunar Tables, but he had them printed at the expense of the British Government and secured for him a personal grant of £1000 against the opposition of Babbage and South, who were on the Board of Visitors for the Observatory.
Airy came into conflict with Prof. Cayley about the kind of questions that ought to be set at the Cambridge Tripos Examination. Airy held that "The papers were utterly perverted by the insane love of problems, and by the foolish importance given to wholly useless parts of algebraical geometry. For the sake of these every physical subject and every useful application of pure mathematics was cut down or not mentioned." When invited to make an address at Cambridge, he seized the occasion to renew the attack; he also wrote to the board of mathematical studies. He wished to introduce into the list of subjects for examination Partial Differential Equations, Probabilities, Mechanics in a form which verges on practical application, Attractions, Figure of the Earth, Tides, Theory of Sound, Magnetism but not (for the present) Mathematical Electricity. In the correspondence which followed Cayley said, "I think that the course of mathematical study at the University is likely to be a better one if regulated with a view to the cultivation of science as if for its own sake, rather than directly upon consideration of what is educationally best (I mean that the best educational course will be so obtained) and that we have thus a justification for a thorough study of pure mathematics. In my own limited experience of examinations the fault which I find with the men is a want of analytical power, and that whatever else may have been in defect Pure Mathematics has certainly not been in excess." Later Airy criticized the questions set for the Smith prizes in 1879 in a letter addressed to the members of the Senate. He singled
