which make one divine age or Maha-yug; seventy-one Maha-yugs make 306,720,000 years, to which is added a sandhi (or the time when day and night border on each other, morning and evening twilight), equal to a Satya-yug, 1,728,000, make a manwantara of 308,448,000 years;[101] fourteen manwantaras make 4,318,272,000 years; to which must be added a sandhi to begin the kalpa, 1,728,000 years, making the kalpa or grand period of 4,320,000,000 of years. As we are now only in the Kali-yug of the twenty-eighth age of the seventh manwantara of 308,448,000 years, we have yet sufficient time before us to wait before we reach even half of the time allotted to the world. These ciphers are not fanciful, but founded upon actual astronomical calculations, as has been demonstrated by S. Davis.[102] Many a scientist, Higgins among others, notwithstanding their researches, has been utterly perplexed as to which of these was the _secret_ cycle. Bunsen has demonstrated that the Egyptian priests, who made the cyclic notations, kept them always in the profoundest mystery.[103] Perhaps their difficulty arose from the fact that the calculations of the ancients applied equally to the spiritual progress of humanity as to the physical. It will not be difficult to understand the close correspondence drawn by the ancients between the cycles of nature and of mankind, if we keep in mind their belief in the constant and all-potent influences of the planets upon the fortunes of humanity. Higgins justly believed that the cycle of the Indian system, of 432,000, is the true key of the secret cycle. But his failure in trying to decipher it was made apparent; for as it pertained to the mystery of the creation, this cycle was the most inviolable of all. It was repeated in symbolic figures only in the Chaldean _Book of Numbers_, {33} the original of which, if now extant, is certainly not to be found in libraries, as it formed one of the most ancient Books of Hermes,[104] the number of which is at present undetermined.