the sound of a signal is ascertained to be most effective in the line of its axis, it follows that the instrument should be capable of such adjustment that its strongest sound may be projected directly against the opposing wind.

"It is to be observed that on another point these experiments confirm the opinions expressed by your committee to America, for, with regard to the question of distinctions, it is clearly shown that it is not possible to rely upon distinctiveness of note alone, for the mariner would not appreciate such a distinction; indeed the siren, horns, and whistles have invariably been spoken of by sailors in the vicinity as "the fog-horns." Between the report of the gun and the sound of the siren or the trumpet there is a perfectly intelligible difference; but for further purposes of distinction for the latter instruments, variation of the length of the silent interval between each blast offers the most satisfactory means. With regard to this point it will be seen that Dr. Tyndall has, with some reservation, expressed an opinion which hardly seems to harmonize with the experience of the Elder Brethren. Dr. Tyndall would restrict the silent interval to a length of 30 seconds, and in support of his opinion draws an analogy between the action of the eye and the ear, which does not commend itself to actual nautical experience. The board will probably not be disposed to waive a clear advantage in power and great scope for distinctiveness, in order that the longest interval of silence should not exceed 30 seconds, especially with the knowledge that guns fired at intervals of a quarter of an hour have proved of great service to the mariner hitherto.

"A general review of the entire report shows that a considerable amount of knowledge has been gained, both as to the influence of the atmosphere in the transmission of sound and to what extent the appliances we possess may be relied on for producing such sounds as will be of practical service to the mariner. We have learned something of our igno rance in regard to sound-transmission. We now know that the varying conditions of the atmosphere render no judg ment infallible, and that conclusions founded on the experience of to-day, are not trustworthy for estimating the results of the morrow. We know, moreover, that after bringing forward all the aid which science can at present give to guide the mariner in thick weather, there is still a large element of uncertainty and mystifying influence with which he has to combat, and which renders it incumbent on him to use the greatest caution and prudence in thick S. Ex. 54———-5

weather, to regard and make use of the sound-signals as means for assuring the vessel's position, and not as aids for running at high speed; and, above all, never to trust so implicitly to sound-signals as to neglect the use of the seaman's best friend and truest guide, the lead.

"The subject of fog-signals has by means of this investigation received a great impetus. It may fairly be said that we have taken a considerable step in advance, and it only remains to follow it up. As we go forward our experience will widen, and although it is more than probable that a few years of practical experience and testing of fog-signals will materially modify our present views, and improve considerably the instruments we have, yet we now know how to go forward and in what direction to head our efforts. It is to be hoped that before very long our coasts will be guarded by a complete chain of sound-signals, all effective and useful to the mariner. No unnecessary delay need now occur before proceeding to supply the light-ships and the important stations already selected by the board, and when they are all established the lights rendered useless at a quarter of a mile by fog will be superseded by sound-signals capable of warning the mariner at a distance of three miles.

"It is almost unnecessary to add that in thus giving practical effect to the spirit of the recommendations of this valuable report, the Elder Brethren will have the satisfaction of knowing they are acting in the highest interests of humanity and conferring an inestimable boon on the nautical community at large."

Location.

Height of focal planes.

Engine-house.

Dwellings.

SOUTH FORELAND.

The great electric lights at South Foreland, two in number, are three miles east of Dover Pier, on the high chalk-cliffs overlooking the Strait of Dover, from which can be seen Grisnez and other French lights. They are about 1,000 feet apart, the high light 372, the low one 275 feet above the sea, and form a range or lead as a guide to clear the Goodwin Sands, one of the greatest dangers in British waters. A general plan of the establishment is shown in Plate I.

A fire-proof engine-house, a plan of which is shown in Plate II, is placed midway between the towers, and contains the magneto-electric machines, the engine-room, boilerroom, coal-room, and two repair-shops. Near by are the dwellings of the engineer who superintends the establishment, and those of some of the keepers, there being six at this station.

tric machines.

of

The electric current is generated by means of large mag- Magneto-elec neto-electric machines, two of which are provided for each light, though habitually in clear weather but one machine is used for each. These machines are driven by means of Manner of operating the belting connected with a steam-engine, a duplicate of which same. is kept for use in case of accident or repairs. The boilers, which are of the ordinary locomotive class, are also in duplicate. About 56 pounds of coke per hour are consumed Coke used. during the night; during the day the fires are banked. One of these electric machines is of French manufacture, Machines having been made by the Compagnie l'Alliance of Paris. The glish others are English-made machines of Professor Holmes's ture. patent, and are considered by the Elder Brethren to be superior, though the French appeared to be the simpler in construction and is the one shown to visitors in explaining the operation of generating the electric current. This operation is fully illustrated in the description, which will be found Description given at La Hève. further on, of the magneto-electric lights at La Hève near the mouth of the Seine.

French and Enmanufac

It may be well to state here, however, that each machine Helices. is composed of ninety-six helices mounted upon six gun

metal wheels, each having sixteen helices.

Between these wheels are placed the magnets, eight in Magnets. each division, forty of which are composed of six layers or leaves riveted together, and sixteen (the end ones) similarly constructed but having only three leaves or layers. These magnets, which are mounted in frames, are stationary, while the helices revolve at the rate of four hundred revolutions per minute.

for operating the

Power of the

The power absorbed by the machine alone, disregarding Power required friction, is four indicated horse-power, and the actual power machines. required to work one of the machines, including the friction. of engine and shafting, is six indicated horse-power. The power of a magneto-electric machine is according to the gross attractive power of its magnets, each magnet hav- machines. ing a certain lifting or attractive power, (expressed in pounds.) In the machines at South Foreland each of the sixplate magnets will lift 108 pounds, and each three-plate magnet will lift 54 pounds, making the attractive power of the magnets in one machine to be 40x108+16×54=5,184 pounds. This may be considered as expressing the power of the machine. The proportion of the lifting power to the actual weight of a magnet is a good indication of its value, and, generally speaking, a magnet which will one-half times its own weight is a good one. magnet at South Foreland has a weight of 43

lift two and Each six-plate pounds, and

Value of mag

nets.