Letter from [William George] Armstrong, Cragside, Rothbury, to [Alan Archibald Campbell] Swinton, 66 Victoria [Street], London, S.W Informs Campbell Swinton where in London he will meet him. States he is glad that Lord Londonderry has followed his advice. Recommends that he be very careful about the motive power and not to leave any form of engine liable to variation of speed. States that by reciprocating engines single cylinders & light fly wheels should be avoided, suggesting he would restrict all use of accumulators as mush as possible. 16 January 1891