THE REVIVAL OF SCIENCE 289 



extraordinary memory for figures. His " Arith- 

 metica Infinitorum " is described as " the most 

 stimulating mathematical work so far published 

 in England." It contained the germs of the 

 differential calculus, and it suggested to Newton, 

 who " read it with delight/' the binomial theorem. 

 In it TT was evaluated, and it must not be for- 

 gotten that to Wallis we owe the symbol for 

 infinity, oo . Living in troublesome times, under 

 many rulers, he contrived, not without some loss 

 of popularity, to remain on good terms with all. 

 His services were, indeed, indispensable to a 

 succession of Governments, for he had a power 

 of deciphering which was almost miraculous. 

 Cromwell, who seems to have had a great respect 

 for his powers, appointed him Savilian professor 

 of geometry at Oxford in 1649. 



Another mathematical ecclesiastic was Seth 

 Ward, Bishop of Exeter and afterwards of Salis- 

 bury. Ward was educated at Sidney Sussex 

 College, and, in 1643, was chosen as mathematical 

 lecturer to the University of Cambridge. But, 

 like Wallis, he was appointed, and in the same 

 year, to a Savilian professorship, that of astronomy 

 another instance, not uncommon at the time, of 

 men educated at Cambridge but recognised and 



