...the said angles of inclination are equal to one another. 9. A solid angle is that which is made by more than two plane angles, which are not in the same plane, meeting at one point. 10. Equal and similar solid figures are such as are contained by similar planes...

....'. it must be their common section AD. DEF.— A solid angle is that which is made by the meeting of more than two plane angles, which are not in the same plane, at the same point PROP. 20.— If a solid angle be contained by three plane angles, any two of them...

...at a point. Euclid's second definition (XI def. 1 1) is "A solid angle is that which is contained by more than two plane angles which are not in the same plane and are constructed to one point." Figure 5 shows a solid angle OABC with three plane angles. There...

...and thickness. 51. Tho boundaries of a solid are surfaces. 52. A solid angle is that which is made by more than two plane angles, which. are not in the same plane, meeting at one paint. 53. A pyramid is a solid figure contained by planes, one of which is the base,...

...the problematic Definition 10: Book XI, Def. ix. A solid angle is that which is made by the meeting of more than two plane angles, which are not in the same plane, in one point.42 And only then did he define similar solid bodies while explicitly omitting the problematic...

...in the same surface, towards all the lines. Otherwise : A solid angle is that which is contained by more than two plane angles which are not in the same plane and are constructed to one point. 12. A pyramid is a solid figure, contained by planes, which is constructed...