Ill 



crushing reply, which he published in the ' Philosophical Magazine ' 

 ^in 1827. 



It is, however, impossible even to mention the names of the many 

 papers of which he was the author. The few which have been men- 

 tioned above prove how soon after his degree he took a leading part 

 in the scientific work of the day. They show also how, from the very 

 beginning, his mind was turned to practical applications, leaving 

 aside any pure theorems of which he did not see the immediate use. 



In 1826 Mr. Airy published his mathematical tracts, which almost 

 immediately became the standard text-book for students in the 

 University. In the first edition we find only the lunar theory, the 

 figure of the Earth, precession and the calculus of variations, the tract 

 on the planetary theory and that on the undulatory theory being- 

 added in the second edition, 1831. As his object was to give a clear 

 statement of first principles, he put into the book just what was 

 wanted at the time he wrote, making his judgment with admirable 

 skill. The student world has now outgrown the book, but this is in 

 part due to the excellence of the teaching of the book itself. The 

 first tract, that on lunar theory, is interesting to Cambridge students 

 for another reason. The attention of the University had been so long 

 confined to the works of Newton that the analytical mode of treat- 

 ment had been almost entirely neglected. The methods of Newton 

 are, Mr. Airy remarks, beautiful, but they have all the imperfections 

 which necessarily accompany first attempts; for the explanation of 

 some of the lunar inequalities they are hardly sufficient, and for the 

 calculation of most they are quite inadequate. For other branches of 

 physical astronomy, such as the planetary theory, their inadequacy 

 has never been questioned. In this tract he endeavours to lay before 

 the student an analytical view of the lunar theory, giviug references 

 to the ' Principia ' to show the connexion between the different systems. 

 The tract on the calculus of variations is the only one which is purely 

 mathematical. Though it does not go very far into the subject, 

 yet the author must have had a deep sense of the power of this 

 calculus, for he has used it in his physical papers, even in places 

 where simpler methods might more naturally have suggested them- 

 selves to his mind. In the preface he speaks of this calculus as the 

 most beautiful of all the branches of the differential calculus, 'l i e 

 excellence of the tract on the undulatory theory is evident when v, e 

 remember the length of time in which it was regarded as the standard 

 text-book of the University. When the other tracts, after a long lite, 

 became antiquated, this one retained its popularity, and has been 

 reprinted several times by itself, and is even yet in use. 



Mr. Airy was elected a Fellow of Trinity College the year after his 

 degree, and later on in life he was chosen one of the three first 

 Honorary Fellows of the College, the others being Thirl wall and 



b 2 



