Bipedal sphere

Late summer or early fall 1975 close to railway about a mile north of London Gatwick Airport I was a15 year old mooching around after dark in unlit parking lot. My buddy had gone to check out something not far away, he said he never saw what I witnessed. A small black sphere no more than 2 1/2 ft high ran past me on two seemingly un jointed legs towards railway into the dark, followed by another one exactly the same a few seconds later. There was no sound and their movement was incredible to see at the time and still is. I guess that's why it's stayed fresh in memory. I had frozen in amazement at the time and never made any official report, not wanting to me treated as a crazy person, back then you could be committed insane for less. Definitely inorganic, a jet black sphere with jointless un tapered legs, no other protrusions, maybe small feet? No sense of any interaction, they just ran past by me within 4/5 feet. They came from direction of an electric substation towards electrified rail is only rational I have for their presence at time, top up charge?