In answer to your communication of the 22nd March (which I return herewith), the Royal Society do not work their electric light installation by means of an "Otto" gas engine. This was done for a time; but I cannot answer your question in detail; I can only say that the method appeared to be an expensive one ^if^ used in connection with accumulators, the chief expense being the rapid degeneration of the cells. At present, and for some time past, we have been supplied from one of the electric centres.
I am, yours truly,
Asst. Sec. R.S. [Assistant Secretary, Royal Society]',