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LIST OF ILLUSTRATIONS 
Letter of Huygens (XXI) of 24 March 1637 • Facing page 40 
Page 1 a of letter of Descartes (XXIV) of 20 May 1637, 
with a marginal note of Huygens „ 4^ 
Page 1 a of letter of Descartes (LIII) of 12 March 1640 „ 130 
Letter of Descartes (LXXXIX) of 2 November 1643 . „ 218 
Page 1 a of letter of Mersenne (CXI) of ry February 1637 „ 262 
Stampioen's Three Points (CXVIII), 23 November 1639 „ 278