Metropolitan drainage. Copies of a communication from the Metropolitan Board of Works to the First Commissioner of Her Majesty's Works, &c., requesting further information relative to the plan for the main drainage of the metropolis suggested in the report, dated 31 July 1857, of Captain Douglas Galton, R. E., James Simpson, Esq., C. E., and Thomas E. Blackwell, Esq., C. E., the referees appointed to consider the question of the main drainage; and of a letter from the referees to the First Commissioner, transmitting further information (in continuation of Parl. Paper, no. 13, of the present session).