( 3045 ) 
may be prefently feen ia one or other of the Files 6f tfiofe 
Roman Numbers. Having then employed thefe bands in 
railing or abafing them on a table, to make thofe principal 
numbers, that arc neceffaryj toappear over againft one ano- 
ther, he further bethought himfelf (for a yet fliorter way,) 
to difpofe thofe pieces into circles very equal , and to gleWg 
upon each of them, 3 or 4 fmall buttons of wood, of the 
bignefs of a pins-head, and then to put them upon a Cylinder 
of wood or paft'board, on which they might be turned by 
means of thofe buttons : Which form made him call this 
\\ti\Q\n^mmtx\X.2LX\ Arithmetical Cylinder^ which is of the big" 
nefs or diameter of a ChildrenssDrumg or of the form of an 
Hat 3 and of what height you will, to hold as many bands 
or circles as you fiiall defire to make greal Operas 
tions. 
Thepraftifeof this Inflrumentis (hewed by divers lxam« 
plesj as may be feen in the Book it (elf. 
III. La DlOPTl^I OCVLAlJlEl par k 
Fere Cherubin Orleans^ Capucm ^ Paris^ 1671« in 
Fol. 
THe Author of this large and elegant Volume, having 
propofed tohimfeif to comprehend in it and to teach 
all that concerns the Theory , Ufe^ and Mechanifm of the 
Telefcope (by him called the Ocular bioptriquej divides it into 
three principal Parts* 
The Firfi contains theDodrine of Opticks and Dioptricks^ 
or,of Simple vifion Diredt, and that which is made by rays 
Refradled i both by him pretended to be handled w;ith a 
fuccintSt, but fiDgular, Method. 
Difcourfing 01 RefraHion, he declares^That the Refra(9:ioa 
of a vifual ray in Glaffe to 50 degrees of inclination, is pro- 
portional to the Inclination of the ray, as far as ferife is able 
to judge of it. And that 3 the Inclination not exceeding 
30 degrees, the Angle of the rcfradlion of the ray, which 
C c cc 2 enters 
