When CT Russell, who would eventually invent the religion that parades under the umbrella name of the Watchtower Society, was a young man in his early 20s, he "got religion" and as a result began to associate with a group of Second Adventists called the Allegheny Second Adventist Church.
The Second Adventists were originally a group of Bible believing fundamentalists led by ex-Baptist William Miller, who had come to believe that Christ would come again, physically and visibly, in 1834 at the latest. When this failed to happen, his movement fragmented into several smaller sects all of which proclaimed their Miller ancestry by subscribing the "Second Advent" name to their particular group. We have no record of how many groups that they finally ended up with, but we know of at least the "Second Advent Christian Church" "The Life and Advent Union" and the one that Russell was associated with. Another and the most sucessful, which has grown even larger than the WTS, was the Seventh Day Adventist Church.
The group that Russell was associated with came to the conclusion, mainly as a result of labyrinthtine biblical investigation, that Miller had been out in his calculations by a generation. Since to these simpletons a generation was a neat 40 years, which is not necessarily true according to the Bible, they concluded that THE date was 1834 + 40 = 1874. This was to be regarded as the final date for Christ's physical, visible return. So we know for a fact then that Russell's original belief was that Christ was to come again in a physical literal form. At the prescribed time, evidently in early October of that year, the faithful gathered on Brooklyn bridge, attired appropriately in white raiment, holding aloft palm branches, in anticipation. Russell was to deny, many years later, that he was ever there, but those present made written affidavites that he was.
When nothing happened for a second time many of these Second Advent groups fell apart, reduced to a dot on the Christian theological landscape. Russell, wealthy enrepeneur that he was, began his own "Bible study" group made up of his employees, tactful enough reason perhaps for them to acknowledge him as "pastor" We do not know what Russell taught at this time concerning the Second Advent, because we have no written records. But in January of 1876, 2 years after the supposed Second Coming, Russell came upon Nelson Barber one of the weightiest of Second Adventist luminaries, and he managed to convince Russell that their chronology was in fact correct. Jesus had returned in 1874.Using a new translation of the New Testament, new at least for that time, the Emphatic Diaglott, Barber showed Russell that the actual Greek word for Coming as used in Mattew 24:4, was "parousia" meaning "presence". So Christ was "present" since 1874, not that he was "coming". The trick was of course, that since no one could see Him, it was concluded that Christ must have come invisibly. Since Russell was a rich young punk [he was 24 years old at that time remember] who knew as much New Testament Greek as a Samarkhand camel trader, he swallowed the Barbour myth, hook, line, and sinker. To his dying day, Russell was to defend his "invisible" return of Christ in 1874. He insisted that he and his followers could "see" this phenomenon. Today the WTS admits that what Russell "saw" was unmitigated rubbish.
In 1926, when the 1874 date became untenable, the then WTS leader, JFR, in casual disregard of the theological integrity of his own beliefs, altered the doctrine to make it say that Christ had actually come invisibly in 1914. [Something that the WTS neglects to tell its followers is that this change was post-positive, not predictive] The current method of teaching this doctrine to new recruits is essentially unaltered since CTR's day, the sole exception being the different date. Because Christ came in 1914, and because no one saw Him, it therefore must mean that He came invisibly.
There is potentially a new doctrinal thrust that is in the offing for the WTS. Hitherto,ever since the time of CTR, it had been concluded that the return of Christ was to last a numerical generation. Despite the theological legerdemain of the WTS to stretch the meaning of "generation" to make it mean whatever they want it to mean, the WTS is faced with the problem of a long-lasting generation. Either they will have to invent a new date, which means that the 607 bc date is discontinued, or they will have to concede, as the Seventh Day Adventists eventually did, that the "invisible" presence is to last a long time.
By the way, the WTS does not teach that Christ actually did return in 1874,1914 or any other unspecified date in the future.. It seems strange to make such a statement, but it is true. Ask a WTS follower that if Christ is "present" here on earth, then who the hell is sitting at God's right hand right now. Hmmm? When Christ went up to heaven, He was never to return to the earth. If Christ is present here on earth AND in heaven, then he must be able to do something that jjjooober supposedly almighty, cannot do, and that is to be omnipresent.
The official theology of the WTS is that the only thing that Christ did in 1914, was to "turn his attention" to the earth. The actual belief of Christ coming again is taught, officially at least, to be be merely a metaphor. That dear reader, is the incredulous teaching of this ignorant group. Evidently till 1914 Christ was sitting and contemplating his navel, then in 1914 he lifted his gaze from his navel and peering down at the earth, managed to accomplish this magical sleight-of hand while all the time remaining sationery back in heaven.
So not only is the Second Coming invisible, its all symbolic anyway. It never literally happened.
Cheers