Note 209 — PART I. INTRODUCTION. (continued 4)

Ten single threads of cotton to each of those 18 lamps, make in all 180: now a street lamp in London, is said to contain 28 single threads, and if we divide 180 by 28, we shall have 6 3/7: hence the oil consumed in the Hunston Light-house, is less than that consumed by 7 London street lamps.—The advantages derived from Mr. Walker’s plan, are, 1. The strength of light may be proportioned to the distance at which it may be necessary to be seen. 2. It may be maintained at a less expence than where the light is equally diffused all round the compass. 3. It requires little attendance. 4. It always appears of the same magnitude—provided, as was above hinted, the glass be kept clean, and the lamps in a proper trim—circumstances that must be attended to, and not neglected.—Here it may be further observed that the improvement of light-houses is not the only subject that has undergone Mr. W.’s close and successful investigation. Many papers written by him, have appeared in Nicholson’s Philosophical Journal, and Tilloch’s Philosophical Magazine, giving an account of divers useful inventions of his, and new discoveries is physics, chiefly under the following heads.—1. On a method of using candles, so as to produce no smoke, nor require snuffing.—2. A method of obviating the effects of thick wires in transit telescopes. 3. On the Plumb line and Spirit level. 4. On the vibrations of pendulums in vacuo. 5. On a standard of light, by which we may compare the strength of any other light. 6. Description of an apparatus for conducting sound, and holding conversations at a distance. 7. Description of a new reflecting quadrant. 8 On the best method of ascertaining the dip of the horizon at sea. 9. On the methods of observing the longitude at sea. 10. On the phenomenon of the horizontal moon. 11. Description of a new cometarium. 12. On transit instruments. 13. On vision. 14. Description of a new optical instrument called a Phantasmascope. 15. Observations on vision, when objects are seen through a mist. 16. On the power of the eye, by which it is adjusted to see objects distinctly at different distances. 17. On the apparent magnitudes of the same object seen under different circumstances. 18. On deal pendulum rods. 19. On the human eye: in which many errors of former writers on vision are pointed out, and the true theory explained.