Note 37 — PART SECOND. NOTES ON THE ILLUMINATION OF LIGHTHOUSES, WITH SHORT NOTICES OF THEIR EARLY HISTORY.

The Drummond light is produced by the ignition or combustion of a ball of lime (³⁄₈ inch diameter) in the united flames of hydrogen and oxygen gases, and is equal to about 264 flames of an ordinary Argand Lamp with the best Spermaceti oil. It derives its name from the late Lieut. Drummond, R. E., who first applied it in the focus of a paraboloïd for geodetical purposes, and afterwards proposed it for Lighthouses. (See his Account of the Light in the Phil. Trans. for 1826, p. 324, and for 1830, p. 383.) The Voltaic light is obtained by passing a stream of Voltaic electricity from a powerful battery between two charcoal points, the distance between which requires great nicety of adjustment, and is the chief circumstance which influences the stability and the permanency of the light. The Voltaic light greatly exceeds the Drummond light in intensity, as ascertained by actual comparison of their effects; but the ratio of their power has not been accurately determined. It was first exhibited in the focus of a reflector by Mr James Gardner, formerly engaged in the Ordnance Survey of Great Britain.