How did brunel's atmospheric railway work?

I am not sure it was invented by Mr. Brunel- who was also a Marine architect ( Great Eastern, among others) and Bridge designer of some note. The idea was a sort of all-weather transit system- which could run underground- and as electric power had not yet been commercially harnessed- Con Ed only dating to l879 ( as Edison Lamp Works)compressed air in a sort of central-track guide rail -something like slot cars in a way, was the motive power. on accidentally attained a speed of 80 Miles per hour- covering a mile in 45 secs- when an overcharge of compressed air- was Dumped into the system. They lasted a while in the mid-nineteenth century, but are long obsolete- still an early attempt at a pollution-free subway system. The Germans had a different type of atmospheric railway using captive balloons and a sort of elevated track system- it was not know if this was ever reduced to reality or remained a sort of science-fiction magazine cover thing- which it did in the Alps.