'Circuit' or 'Circuitt' is referred to as a friend of the publisher William Heinemann. Together they travelled to Corsica where they met JW in 1901.
Circuitt was probably the Arthur John W. Circuitt recorded in the census of 1881 as living with his mother Mary Circuitt at 65 Gloster Street in London. He was then a bank clerk. There home in fact was above a branch of Lloyds Bank. Later, when he knew JW, he may have worked at the Union Discount Company at 39 Cornhill, London, EC (see JW's note of the address, #13389).
Kelly's London Postal Directory, London, 1893; UK census, 1881, from http://www.familysearch.org (accessed 2004).