iv.] CHOICE OF A PROFESSION, 1831. 73 



his minerals. Astonished at the vast range of his library 

 in subjects and language. Took a kind farewell of him 

 and Sedgwick, and went to hear Airy's lecture before 

 setting out. It was upon hydrostatics and pneumatics. 

 Took leave of Mr. Peacock, Mr. Ramsay, and Mr. Thorp, 

 and proceeded by coach to London more than delighted 

 by my stay at Cambridge. 



' I omitted to mention one of the finest mechanical 

 illustrations of an abstruse theory that I ever saw, at 

 the Observatory, contrived by Professor Airy. It was to 

 explain how, on the theory of undulations, the coinci- 

 dence of two undulations will polarize light in one plane, 

 the semi-coincidence in a plane at right angles to the 

 former, and by a difference of a quarter of an undulation 

 polarize it circularly. . . . 



* Persons to whom I was introduced at Cambridge : 

 Professors Sedgwick, Whewell, Airy, Henslow ; Mr. Pea- 

 cock, Thorp ; Dr. Ramsay, Vice-Master of Trinity ; Mr. 

 Jarre tt, Romilly, Bowstead, Ash, Turner, Bothman, 

 Thirl wall, Hare, Sheepshanks/ 



A visit to Mr., afterwards Sir John Herschel, is thus 

 recorded : 



'May 27th. Went by appointment to Slough to see 

 Mi. Herschel. Met Mr. Beaumont, who is setting up 

 astronomer. Herschel was engaged most of the afternoon 

 in putting his twenty-feet reflector in order for the even- 

 ing, in case we should have the good fortune to have any 

 observations. Mrs. Herschel was unwell, and I did not 

 see h-r. \\'e dined, and the sky Ix^an to look favour- 

 able after a cloudy day. As soon as it was dark, we went 

 to the telescope, just furnished with a beautiful new 

 -li.-d .-|MTiilinn, which had not been used before. We 

 got hold of Saturn, and, notwithstanding a very indiffer- 

 sky, saw him in a manner which was very delightful 

 tome. His body was l>ut mdifierentlY defined, 1 



however, distinctly tin- >hado\v of hi- rin-4 and five satel- 



. which is all that h i been seen with the 



telescope. Speedily, alas ! the sky clouded 



