Correspondence and papers regarding the determination of the longitude of Brussels by observing set stars and taking the difference between the local time and Greenwich Time received by telegraphic signal. The material includes Airy's paper 'Difference of longitude between the Observatories of Brussels and Greenwich as determined by galvanic signals'; a similar piece for 'The Athenaeum'; instructions to those involved and to the Submarine and European Telegraph Company; comparisons of the observations of galvanic signals made by different observers, with an abstract of the comparisons; compared clock times at Greenwich and Brussels; papers on the formation of Greenwich sidereal times and abstracts; and comparisons of sidereal times at Brussels and Greenwich. The papers include correspondence with J.C. Clark, E. Dunkin, L.A. Quetelet and E. Sabine.