Letter, from William Nairn Forbes to Sir John Herschel, dated at Calcutta Mint Autograph letter signed by sender. Appreciation of John Frederick William Herschel's son [John]. Admired John Frederick William Herschel's letter of 2 Feb. 1852 to Treasury, in which William Nairn Forbes's most important recommendations [to 1848 committee for Mint reform] have been carried out. Dependence on steam for transportation has raised price of coal. Proposes two methods to replace coal: (a) use electrical conductivity of seawater in presence of dissimilar metals to propel ships, and (b) generate heat in 'Earth Batteries,' similar to dungheaps. Asks John Frederick William Herschel to approve request by John Gilbert, retired mechanical engineer at Calcutta mint, who wishes to visit Royal Mint, but was refused several years ago. 18 February 1854