The idea, as I understand it, is to transfer fragile material (glass bulbs in this case, I believe) from one moving something to another, or over to a platform. This is taking place in the 1920's, I think. Anyway, here's the quote:
However, I suffered myself to be taken to Battersea; and there, sure enough, I found a workshop, duly labelled as the premises of The New Transport Company, Limited, and spacious enough to accommodate a double railway line with a platform. The affair was unquestionably real, so far.
The platform was not provided with a station: its sole equipment was a table with a row of buttons on it for making electrical contacts. Each line of railway had on it a truck with a steel lid. The practical part of the proceedings began by placing an armchair on the lid of one of the trucks and seating me in it. A brimming glass of water was then set at my feet. I could not imagine what I was expected to do with the water or what was going to happen; and there was a suggestion of electrocution about the chair which made me nervous.
Gattie then sat down majestically at the table on the platform with his hand hovering over the buttons. Intimating that the miracle would take place when my truck passed the other truck, he asked me to choose whether it should occur at the first passage or later, and to dictate the order in which it should be repeated.
I was by that time incapable of choosing; so I said the sooner the better; and the two trucks started. When the other truck had passed mine I found myself magically sitting on it, chair and all, with the glass of water unspilled at my feet.
Does "a double railway line" mean two tracks running parallel to each other? Are they linked? Is a switch involved?
Are the trucks - trucks (i.e. bogies) that look like this:
or are they flatbed freight cars that look like this:
- Most important: how was the author (G.B. Shaw) transferred (along with the glass of water) over to the other - moving - whatever it was?

