22. TYCHO'S LARGE SEXTANT 48 23. THE QUADRANT IN URANIBURG 49 24. TYCHO'S FORM OF TRANSIT CIRCLE 50 25. A MODERN TRANSIT CIRCLE 51 26. ORBITS OF SOME OF THE PLANETS DRAWN TO SCALE 60 27. MANY-SIDED POLYGON OR APPROXIMATE CIRCLE ENVELOPED BY STRAIGHT LINES 61 28. KEPLER'S IDEA OF THE REGULAR SOLIDS 62 29. DIAGRAM OF EQUANT 67 30. EXCENTRIC CIRCLE SUPPOSED TO BE DIVIDED INTO EQUAL AREAS 68 31. MODE OF DRAWING AN ELLIPSE 70 32. KEPLER'S DIAGRAM PROVING EQUABLE DESCRIPTION OF AREAS FOR AN ELLIPSE 71 33. DIAGRAM OF A PLANET'S VELOCITY IN DIFFERENT PARTS OF ITS ORBIT 72 34. PORTRAIT OF KEPLER 76 35. CURVE DESCRIBED BY A PROJECTILE 82 36. TWO FORMS OF PULSILOGY 87 37. TOWER OF PISA 91 38. VIEW OF THE HALF-MOON IN SMALL TELESCOPE 97 39. PORTION OF THE LUNAR SURFACE MORE HIGHLY MAGNIFIED 98 40. ANOTHER PORTION OF THE LUNAR SURFACE 99 41. LUNAR LANDSCAPE SHOWING EARTH 100 42. GALILEO'S METHOD OF ESTIMATING THE HEIGHT OF LUNAR MOUNTAIN 101 43. SOME CLUSTERS AND NEBULÆ 102 44. STAGES OF THE DISCOVERY OF JUPITER'S SATELLITES 103 45. ECLIPSES OF JUPITER'S SATELLITES 105 46. OLD DRAWINGS OF SATURN BY DIFFERENT OBSERVERS, WITH THE IMPERFECT INSTRUMENTS OF THAT DAY 111 47. PHASES OF VENUS 112 48. SUNSPOTS AS SEEN WITH LOW POWER 113 49. A PORTION OF THE SUN'S DISK AS SEEN IN A POWERFUL MODERN TELESCOPE 114 50. SATURN AND HIS RINGS 115 51. MAP OF ITALY 118 52. PORTRAIT OF GALILEO 126 53. PORTRAIT OF DESCARTES 148 54. DESCARTES'S EYE DIAGRAM 151 55. DESCARTES'S DIAGRAM OF VORTICES FROM HIS "PRINCIPIA" 152 56. MANOR-HOUSE OF WOOLSTHORPE 162 57. PROJECTILE DIAGRAM 170