H.P. Blavatsky Collected Writings, Volume 13 Page 301
[ON COSMIC CYCLES, MANVANTARAS, AND ROUNDS]
[The MS. of this unfinished essay, in H.P.B.’s handwriting, exists in the Adyar Archives. Some of its pages are missing, and some of the sentences are broken off. There is no definite clue in it which would help to determine the date at which it was written, except for the fact that a footnote mentions the sixth and seventh editions of Isis Unveiled. This MS. contains numerical relations and data not mentioned by H.P.B. anywhere else in her writings. It contains important keys which some students might be able to apply to various cosmological problems arising in their individual studies. The most noteworthy point in connection with this MS. is that it is written in two different handwritings, one of which is larger and more rounded than H.P.B.’s ordinary one. It was originally published in The Theosophist, Vol. LXXIX, March, 1958, pp. 36772.—Compiler. ]
Since the total period of the existence of our Planetary Chain (i.e., of the Seven Rounds) is—4,320,000,000—and we are now in the 4th Round; and since we have unto the present Terrene year period 1,955,884,685 years from the beginning of the Cosmic Evolution of Planet A; therefore, in point of time, we shall reach the middle point, or just 3½ Rounds in 204,115,315 years, although in point of space we have virtually reached it being on planet D and in our 5th race.
No. 2 of Agreement.
Since it is said that a Day of Brahma (representing or covering the totality of the Seven Rounds)—equals 14 manvantaras plus a Satya Yug; or 4,320,000,000; but as the Kali Yug covers only 4 Yugas, whereas there are 7—and therefore the correct sum. . . . .*
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* [MS. breaks off at this point.]
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The astrological work states, that:—
3. “The number of years that elapsed since the beginning of Vaisvasvata Manvantara—equals 18,618,725 years.”
The Secret Doctrine tells us that:—
The number of years passed, since the Dhyan Chohan, known in India as Manu Vaivasvata, inaugurated the human Manvantara on our planet D, in the present Round—equals 18,618,725 years.*
For purposes of comparison, and to make, at the same time, some of the Sanskrit expressions clearer, we will now quote from Isis Unveiled what is said therein of the Hindu Kalpas.
“The Vrihaspatis, or the periods called yugas, and Kalpas, are lifeproblems to solve. The SatyaYuga and the Buddhi† cycles of chronology would make a mathematician stand aghast at the array of ciphers. The MahaKalpa embraces an untold number of periods, far. . . . . ‡
The exoteric Brahmanical works give 4,320,000,000 years as the duration of a great Kalpa, a “Day of Brahma.” This includes all the seven “Rounds” of our Planetary Chain, i.e., the period of human existence on different planets in different Rounds together, with what are called “Obscurations” or the period of rest for humanity between two planets, in its passage from the one to the other, after its seven Races are evolved on that planet. It also includes the period of Sandhi (twilight) which is equal to one Satya Yuga. If we take the above figure, as our basis, according to certain mathematical series, explained further on, we obtain the following results:—
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* See further on the Series of the Manus quoted from the July Theosophist of 1883. [See S.D. II, p. 69]
† We take this opportunity of correcting the many typographical errors found in Isis. Having been stereotyped on plates, all the six or seven editions of the work had to be reproduced with their primitive errata.
‡ [It is evident that a page or more of the MS. is missing at this point. The sentence in Isis Unveiled, Vol. I, pp. 3132, ends with the words: “ . . . . . back in the antediluvian ages.” It is interesting to note that H.P.B. altered “Buddhistic” into “Buddhi.”—Compiler.]
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Years 

First Round—  154,285,714 
Second Round—  308,571,428 
Third Round—  462,857,142 
Fourth Round—  617,142,856 
Fifth Round—  771,428,570 
Sixth Round—  925,714,284 
Seventh Round—  1,079,999,998 
4,319,999,992* 
We have thus 617,142,856 years as the period of our Fourth Round. And as the “Night of Brahma” or period of Rest, is always equal to the “Day of Brahma” or the period of activity on each planet,—the period of activity in this 4th Round equals—308,571,428 years. It thus exceeds the period of duration given for our Manvantara (308,448,000 y.) in the Brahminical calculations, only by 123,428, years; and this would be made away with, if in making this calculation we had deducted from it the overlapping of the period of Kalpa which is equivalent to one Satya Yuga and which the Brahmins for purposes of esoteric secrecy have added to the “Day of Brahma.” . . . . . the same arithmetical progression, as above and explained† further on, the following is the duration of humanity on each Planet in our fourth Round, during the period of its activity:
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*It will be obvious that for the purpose of having round numbers, we have, in our calculations, omitted fractions. Thus on the whole “day of Brahma” we have left off a period of eight years. It should also be noted that each “Round” period in the above table signifies both the period of planetary Activity and interplanetary Rest.
† [The MS. is damaged at this point, and the full meaning of the sentence has been lost.—Compiler.]
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Years 

Planet A  11,020,408 
Planet B  22,040,816 
Planet C  33,061,224 
Planet D  44,081,632 
Planet E  55,102,040 
Planet F  66,122,448 
Planet G  77,142,856 
308,571,414* 
Now, it will be seen that 44,081,632 years is the Human Period of Activity of our Planet in this Round. Applying to this period, the same ratio as above, explained further on, we obtain the following results:—
DURATION OF EACH RACE IN OUR ROUND
ON OUR PLANET 

First Race  1,574,344 
Second Race  3,148,688 
Third Race  4,723,032 
Fourth Race  6,297,376 
Fifth Race  7,871,720 
Sixth Race  9,446,064 
Seventh Race  11,020,408 
44,081,632 
The reader will observe that in the above calculations we have given the key to the understanding of these different periods. Till now, the exoteric works only gave the period of the day of Brahma, without either giving the other
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* For the sake of having round numbers, we are again obliged to leave off fractions and hence there is a slight difference. This figure when doubled, will give 28 years less than the 4th Round period mentioned above. Here in the period of activity we have a difference of only fourteen years.
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periods which might help toward the discovery of the Secret, or giving that key itself which might give the results now shown above. But if we have the period of the Day of Brahma and if we know that there are seven rounds, that each round covers seven planets, that the period of rest of a planet in every round equals that of its activity, and if to all this knowledge we apply the key of the septenary arithmetical progression series, then we get the numbers as given above. There is a gradual rise of, from one to seven. The duration of the existence of humanity during the Seven Rounds is 1: 2:3:4:5:6:7. In each Round, the duration of the existence of humanity, on the seven planets of our chain is 1: 2:3:4:5:6:7. The period of human existence in seven races, on one planet, is again 1: 2:3:4:5:6:7. Now, as the planet evolves the 7 races in succession, before humanity can pass on to the next planet, the interval between the disappearance of humanity from one planet and its reappearance on the next, is equal to its existence on the planet which it has just left. Take then 4320 millions as the day of Brahma, and calculate according to the above explanation and you will arrive at the above given results. It is noteworthy that in the Hindu exoteric works the period of the Manvantara (One Round) is given at 308 millions, to speak in round numbers. Now two reasons may be assigned for the adoption of that course. In the first place, the duration of the 4th Round according to the above calculations is 617 millions again, to use a round figure. Now, we have already stated that the period of activity of the planetary chain in one round is equal to its period of rest during the same round, while humanity rests in its passage from planet to planet. Thus divide the period of the 4th Round, into two equal parts; and you have 308 millions and odd as the Manvantaric period of our Round. Thus our Round period may have been in the first instance taken as the Manvantaric period. The Second reason may be this. Our planet being the exactly middle period and we being in the middle of the seven rounds, our round period may have been taken to denote the average Manvantaric period, thus at the same time giving a key in a veiled form to the mystery of the geometrical progression We have already stated that the
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above figures are exact, if the exoteric calculations of the Brahmins about the day of Brahma be correct. But we may again state here that that figure is not correctly given out in exoteric numbers. We may, however, add that the explanations given by us about the progressions, etc., are facts and can be faithfully utilized when anyone of the above described figures are correctly known—in calculating all the rest of the figures. And these processes we have explained because we know that not one of the exact numbers will ever be given out, as they pertain to the Mysteries of Initiations and to the Secrets of the occult influence of Numbers.
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