The Founding of the Modern Theosophical Movement
New York, September 7 th, 1875
September 7th can be seen as the birthday of the theosophical movement. In September 7th, 1875, in the place where HPB lived in New York, 17 persons heard a lecture by George H. Felt on the “Lost Canon of Proportion” of Egyptians, Greeks and Romans.
After the lecture, it was decided to create a Society to continue those studies. William Judge moved that Henry Olcott be elected president, and he was; and Olcott moved that Judge be elected Secretary, and so he was.
Among those present were two distinguished Jewish religion scholars (one of them the editor of an organ of reformed Jews); several spiritualists; a high-ranking mason; one physician and two or three lawyears. 
In a book which belonged to H.P. Blavatsky – “A Guide to Theosophy” – there is a description of the movement’s creation, with the statement that the Theosophical Society was founded in 17 November 1875. To that, at page 51 of the volume, HPB added, in ink:
“Formally; Yet in truth it was founded on 7th September 1875 at my house in 46 Irving Place, New York.” 
And Boris de Zirkoff, the editor of H.P.B.’s Collected Writings, writes:
“There seems to be no reason (…) to doubt that the actual formation of the Theosophical Society took place on September 7th, 1875 (…).” 
In spite of the importance of the meeting held September 7th, it was only on the next evening, on September 8th, that those people made their first meeting with Minutes and written resolutions, and formally decided to make a constitution and by-laws.
As we read the opening lines of the Minutes, written by W. Q. Judge and signed by himself and Olcott, we can also see the importance of the Jewish Cabalah in those initial, inaugural moments of the movement:
“In consequence of a proposal by Col. Henry S. Olcott, that a Society be formed for the study and elucidation of Occultism, the Cabalah, the ladies and gentlemen then and there present resolved themselves into a meeting…”
On 17 November, when H.S. Olcott made his inaugural speech as president, the Society and the movement had already been created, therefore. Although November 17th has been the date more conventionally publicized as the birthday of the movement, the meeting of September 7th produced the decision and impulse. September 8th also has a decisive importance as the date of the first meeting of which there was a written document.
 See the volume “HPB, The Extraordinary Life & Influence of Helena Blavatsky, Founder of the Modern Theosophical Movement”, by Sylvia Cranston, G.P. Putnam’s Sons, New York, 1994, 648 pp., Part Four, Chapter Seven, pp. 143-148.
 “Formation of the Theosophical Society”, a text by Boris de Zirkoff, in “Collected Writings of H.P. Blavatsky”, TPH, Adyar, India, Volume I, 1988, 570 pp., see p. 123.
 “Formation of the Theosophical Society”, in “Collected Writings of H.P. Blavatsky”, volume I, p. 122.