Also full diagonal to edge as 297 to 198, nearly. A peculiarity of this pyramid is, that base is to altitude as apothem is to half base. Thus, 40 : 25 :: 32 : 20; that is, half base is a fourth proportional to base, apothem, and altitude. § 5. THE EXACT DIMENSIONS OF THE PYRAMIDS. R.B. Cub. Brit. Ft. Fig. 15. Cheops. 452 = 761·62 287·767 = 484·887 Fig. 16. Cheops. 365·9047 = 616·549 430·058 = 724·647 639·2244 = 1077·093 Figures 15 to 20 inclusive, show the linear dimensions of the three pyramids, also their angles. The base angles are, Cheops, 51° 51′ 20"; Cephren, 52° 41′ 41″; and Mycerinus, 51° 19′ 4″. R.B. Cub. Brit. Ft. Fig. 17. Cephren. 420 = 707·70 275·61 = 464·40 Fig. 18. Cephren. 346·50 = 583·85 405·16 = 682·69 593·97 = 1000·84 R.B. Cub. Brit. Ft. Fig. 19. Mycerinus. 210 = 353.85 168 = 283.08 Fig. 20. Mycerinus: 131.14 = 220.97 198.10 = 333·7985 296·9848 = 500·42 In Cheops, my dimensions agree with Piazzi Smyth--in the base of Cephren, with Vyse and Perring--in the height of Cephren, with Sir Gardner Wilkinson, nearly--in the base of Mycerinus, they agree with the usually accepted measures, and in the height of Mycerinus, they exceed Jas. J. Wild's measure, by not quite one of my cubits. In my angles I agree very nearly with Piazzi Smyth, for Cheops, and with Agnew, for Cephren, differing about half a degree from Agnew, for Mycerinus, who took this pyramid to represent the same relation of [Pi] that P. Smyth ascribes to Cheops (viz.: 51° 51′ 14·″3), while he gave Cheops about the same angle which I ascribe to Mycerinus. I shall now show how I make Cephren and Cheops of equal bases of 420 R.B. cubits at the same level, viz.--that of Cephren's base. John James Wild made the bases of Cheops, Cephren, and Mycerinus, respectively, 80, 100, and 104·90 cubits above some point that he called Nile Level. His cubit was, I believe, the Memphis, or Nilometric cubit--but at any rate, he made the base of Cephren 412 of them. I therefore divided the recognized base of Cephren--viz., 707·75 British feet--by 412, and got a result of 1·7178 British feet for his cubit. Therefore, his measures multiplied by 1·7178 and divided by 1·685 will turn his cubits into R.B. cubits.