Patti -
I think you're asking if the Barnabas we're currently seeing on the show somehow travelled thru time to be in 1840; as of course he actually was alive in that year.
When Julia first got to 1840 (via the stairway thru time), she insisted on unchaining Barnabas from his coffin, against the better judgment of Ben Stokes. As Ben predicted, the 1840 Barnabas, not knowing Julia, was closer to the ruthless, vengeful and predatory Barnabas of late stage 1795/96 than the 'modern' Barnabas that Julia knew.
After this, it was the 1840 Barnabas who bit Roxanne, and was pretty much planning to kill Julia. Just as he was about to choke the life out of the good doctor, he fell to the floor unconcious. When he opened his eyes, he was posessed by 1970 Barnabas, who had travelled to 1840 to posess his body via the I-Ching.
Hope this answers your question!
CB