It might not be possible, at this late date, to identify the originator of the "floating table," or more correctly (in the contemporaneous vernacular) the "table levitation." It's safe to say, though, that it originated with the resurgence of the movement -- inspired by the Fox sisters -- to communicate with ghosts, which came, of course, to be known as Spiritualism.
Eusapia Palladino was, without question, the queen of the table rappers and levitators, and it may well be she who "invented" the technique. There are numerous accounts of her having performed the phenomena in both magic and early psychic research literature. The first account of her lifting a table mentioned in print was, I believe, in 1888.
The first account of a magician duplicating the feat I've encountered is described in Burlingame's " Leaves From Conjurers' Scrap Books," published in 1891. In a chapter entitled " Second-Site Artists ," Burlingame writes: "An exceedingly clever performer in the anti-spiritualist line, is Prof. Marvelle. He has displayed a great deal of genius in his tricks and apparatus, which has not been confined to magic alone... He excels in anti-spiritualist work, such as rope-tying, slate-writing, materialization, table lifting [emphasis mine] and mind-reading..."
Hope this helps.
Official Historian, Psychic Entertainers Association (I knew I'd be able to use that title somewhere :p )
PS As it's mentioned above, I thought I'd also mention, for those interested, that the term "Second Site" did not originally apply to mind readers or psychics. In ancient British folklore, those endowed with "second site" were the only ones capable of actually seeing Fairies. This all changed, of course, when Sir Arthur Conan Doyle published the famous pictures of the winged creatures, photographed by an adolescent Cottingley girl.