Letter from Charles James Buchanan Riddell, Woolwich to Humphrey Lloyd Riddell sent Lloyd the curves of the May and August term days, and curves of the daily variation. Discussion on the declination curve. If Lloyd would like observations every six minutes, Riddell discusses the way the curve may be used. The St Helena returns have arrived and Riddell points out some of [John Henry] Lefroy’s remarks. Discussion to obtain the points of scale on the magnetic axis. Riddell intends to write to Lefroy at beginning of next week. 30 July 1841