Results arrived at by Professor

portion of the light is exfocal, the divergence is so much increased that the above results would be very far from holding good in practice.

I should further add in regard to photometric experi Tyndall on ex- mental comparison between oil and Wigham's gas-burners for light-houses that Professor Tyndall arrived at the fol lowing results:

periment.

(The four-wick lamp being taken as the unit, the illumi nating power of the gas-flame is expressed in terms of that unit.)

The above experiments ante

improvements in

That is to say, the photometer showed the 28-jet flame to have two and one-half times, the 48-jet flame four and onehalf times, the 68-jet flame six times, the 88-jet flame nine and three-fourths times, and the 108-jet flame thirteen times the illuminating power of a four-wick flame of a first-order sea-coast light-house lamp.

It should be mentioned in this connection that these exrior to recent periments were probably made anterior to the improvement lamp-burners. in oil-lamps made by Mr. Douglass, the present power of his four-wick lamp as compared with the lamp formerly used being as 328 to 269.

COST OF WIGHAM'S GAS-LIGHT APPARATUS FOR LIGHT

HOUSES.

Cost of appara. Mr. Wigham informed me that the cost of gas-making tus packed for shipment and de. apparatus of a size similar to that used at the Irish stations, pool.

Rockabill, Wicklow Head, Hook Tower, and Minehead, packed and delivered at Liverpool ready for shipment. would be, for a single tower, about £1,000, ($5,000,) and for Resulting cost a station with two towers, like that at Cape Ann or Highof placing gas-lands of Navesink, about £1,600, ($8,000.) These esti Ann, or Nave- mates include furnaces, retorts, gas-holders, and tanks for the same, together with the burners and every other item of expense except the freight from Liverpool to America the cost of erection at the site, and the additional buildings

lights at Cape

sink.

buildings.

which Mr. Wig.

sent to erect a

tus in the United

required. The expense of the latter item is, in Ireland, Expense of about £250, ($1,250,) and in the United States would be somewhat larger in consequence of the higher price of labor. Mr. Wigham further stated that he would personally in Conditions on spect any site at which the United States Government ham would conmight desire to use his apparatus, and give the Board all gas-light appara the information and assistance in his power, on condition States. that his traveling and other expenses be paid; also that he would bring with him for the purpose of assisting in and superintending the erection of the entire work, one of his most competent foremen, the charge for whose time would be 108. 6d. ($2.62) per day in addition to his expenses for board, lodging, and traveling.

In regard to the use of his gas-light in the United States Mr. Wigham stated that although his patent did not extend to this country he would have no hesitation in building a gas-light for our use, having no fear but that, should others be required, his labors for the improvement of light-house illumination would be recognized and rewarded.

COST OF THE TRIFORM-LIGHT APPARATUS.

The cost of this gas-apparatus is greater by about £250 Cost of triform ($1,250) than for the ordinary single-light apparatus.

gas-apparatus.

ing ordinary ap

triform.

The expense of removing the upper and lower catadiop-, Cost of chang tric prisms of the lens and substituting for them two refract- paratus for the ing belts is in Ireland not great, as Chance, Brothers & Co., who supply most of the lenticular apparatus for the British lights, offer to take the prisms of the first-order lens in exchange for refractors on payment of a difference of £150, ($750,) provided the prisms are of their own manufacture.

paratus less than

If a new light-house were building, or if a new dioptric Cost of placing apparatus were to be placed in an existing light-house, it triform lens-apwould be rather less expensive to have it arranged on the that of the ordi triform system than in the ordinary way, with a central belt and upper and lower catadioptric prisms.

COST OF MAINTENANCE OF GAS-LIGHTS.

nary kind.

fuel.

The use of tar for fuel in Great Britain within the last Use of tar for few years has so lessened the cost of production of gas that it may be calculated, it is stated, not to exceed, even at outlying stations, 10s. ($2.50) per thousand feet, including 4 per cent. interest on the original outlay for apparatus.

Approximate anuual cost of

If gas could be supplied to our light-houses at this rate, the cost per annum to a first-order seacoast-light, burning gas. habitually 28 jets during the average period of illumination,

Cost of annual consumption of

oil.

(4,311 hours,) would be $550; adding for an extreme case (as West Quoddy Head on the coast of Maine for example) 20 per cent. for additional consumption in foggy and thick weather, we have $660 as the approximate annual cost of the gas for such light.

The annual consumption of oil in our light-houses of the first order is about 760 gallons, amounting at the last aver age contract-price of 89 cents per gallon to $676.40. Less cost for At stations with two towers the cost per thousand feet is feet at stations considerably less than at single tower-stations, since the cost than where there of the labor and other items is proportionately less the greater the quantity manufactured.

gas per thousand

having two lights

is but one.

Beacons on outlying rocks.

Drying gas with chloride of calcium.

The invention not yet fully tested.

Opinions of the

the economy of

ILLUMINATION OF BEACONS BY GAS.

Mr. Wigham has devised an arrangement for lighting by gas, beacons on detached rocks which are inaccessible during heavy weather. Gas for the illumination of such posi tions cannot ordinarily be carried in submarine pipes, on account of the condensation of moisture within the pipe, the lowest part thus becoming filled with water and the flow of gas being consequently obstructed.

Mr. Wigham's plan is to dry the gas by chloride of cal cium, and he proposes to light and practically extinguish the beacon by means of variations of the pressure of gas in the supply-pipe; that is to say, a high pressure of gas, say of six inches of water, closes a stop-cock at the beacon and keeps it closed during the day; at the time of lighting, this pressure is decreased to the ordinary working-pressure of, say, three inches of water, and the cock opens. The burner is lighted by means of a little flame supported by a small "by-pass," such as preserves the light from extinguishment during eclipses at the Wicklow Head intermittent light heretofore described. The full power of the light can be kept up till sunrise, when the increased pressure of gas closes the cock and extinguishes the beacon.

Experiments sufficient for determining the utility of this invention have not yet been made; but it seems a step in the right direction, and affords another indication of the ingenuity of Mr. Wigham.

In concluding my remarks on the subject of gas as an Irish Board as to illuminant for light-houses, I will only say that the Irish gas-lights. Board and its officers state most positively that the actual use of gas at five of its sea-coast stations proves it to be Annual saving more economical than oil, and specifically, at Howth Baily at Howth Baily. the saving is £50 ($250) annually, taking into account all