Tony Wigg makes some interesting observations about 'cycling' on The Heath...
"During the mid 1970's I recall cycling was not permitted on the Heath. It was only during the late 70's early 80's that Hampstead Heath saw designated cycle paths appearing as part of the wider management of the Heath. To my eye the photo, The Cycle Path (above left) shows good evidence that the Viaduct was used for cycling in 1910, so here is my reasoning....
If we look at the photo "The Viaduct Hampstead Heath Photographed from an Aeroplane" (first left), we can see the same white curved fencing either end of the viaduct. Part of this low white picket fence can also be seen in the "Hampstead Heath "In Winter" 1909 picture (second left).
Today an iron railing has replaced this white fence.
The camera is situated on the North end of the viaduct looking south, the four pillars & 4 side support tops are easier to see once the viaduct has been identified.
Looking at the earlier Viaduct Picture (third left) we can see no white fencing thus indicating it to be a later addition. One can just visualise the wayward carefree Edwardian cyclist, oblivious to the steep embankment, the murky Fleet Pond waiting below.
The view ahead is surely a good chance to accelerate and get up some speed....Were these railings prevention or cure? This is the real question."