Millerism
From 1840 onwards, Millerism was transformed from an "obscure, regional movement into a national campaign." The key figure in this transformation was Joshua Vaughan Himes, the pastor of Chardon Street Chapel in Boston, Massachusetts, and an able and experienced publisher. Though Himes did not fully accept Miller’s ideas until 1842, he established the fortnightly paper Signs of the Times on February 28, 1840, to publicize them.
Despite the urging of his supporters, Miller never personally set an exact date for the expected Second Advent. However, in response to their urgings, he did narrow the time-period to sometime in the Jewish year beginning in the Gregorian year 1843, stating: "My principles in brief, are, that Jesus Christ will come again to this earth, cleanse, purify, and take possession of the same, with all the saints, sometime between March 21, 1843, and March 21, 1844." March 21, 1844, passed without incident, and further discussion and study resulted in the brief adoption of a new date (April 18, 1844) based on the Karaite Jewish calendar (as opposed to the Rabbinic calendar). Like the previous date, April 18 passed without Christ's return. Miller responded publicly, writing, "I confess my error, and acknowledge my disappointment; yet I still believe that the day of the Lord is near, even at the door."
In August 1844 at a camp-meeting in Exeter, New Hampshire, Samuel S. Snow presented a message that became known as the "seventh-month" message or the "true midnight cry." In a discussion based on scriptural typology, Snow presented his conclusion (still based on the 2300 day prophecy in Daniel 8:14), that Christ would return on, "the tenth day of the seventh month of the present year, 1844." Again, based largely on the calendar of the Karaite Jews, this date was determined to be October 22, 1844.
Read more about this topic: William Miller (preacher)