798] 
WALLIS. 
643 
interesting surface; it is a ruled quartic surface, the equation of which may be written 
c-y- = (c — zf (a 2 — X-). 
Among the letters in volume III., there is one to the editor of the Leipsic Acts, 
giving the decipherment of two letters in secret characters. The ciphers are different, 
but on the same principle: the characters in each are either single digits or com 
binations of two or three digits, standing some of them for letters, others for syllables 
or words,—the number of distinct characters which had to be deciphered being thus 
very considerable. 
For the prolonged conflict between Hobbes and Wallis, see the article Hobbes, 
[Encyclopaedia Britannica, ninth edition,] vol. xn. pp. 36—38. 
END OF VOL. XI. 
CAMBRIDGE : PRINTED BY J. AND C. F. CLAY, AT THE UNIVERSITY PRESS.