First,
I must point out that Rodel is on Harris, rather
than Lewis (although they are on the same island),
at its south eastern tip.
Andy
Fish found
this information about it on Canmore, the National
Record of Historic Environment.
There
you will see that it was a hydro powered
generator/turbine house, with its supply pipe and
machinery of second world war vintage still in place
at the time of Professor Hume’s visit. There are
several historic pictures from 1976 and more recent
ones from 2011 as well as detailed information on
that website.