Faraday report to Trinity House   14 June 1838

Improvement of Lights

Professor Faraday’s Report on Mr. Gurney’s Oxygen Wire Gauze Lamp. - dated 14th June 1838.

To the Master, Deputy Master¹, and Elder Brethren of the Trinity Board.

My Lords & Gentlemen

I have the honor to report at this time upon a lamp constructed by Mr. Goldsworthy Gurney, fed by oxygen as a supporter of combustion, but different in its arrangement from that described and referred to in my former report.

In the present lamp the oxygen is sent into a hollow cylinder (coloured blue in the section) and is from thence distributed in upright jets or streams through 40 small holes in the upper edge of the cylinder. Within and without this oxygen chamber are two other cylinders forming the walls of the oil chamber the fuel being represented by the yellow colour in the Section above²; and in connexion with this oil, are two large cylindrical wicks, one on the inside and the other on the outside of the oxygen chamber, being represented in the sketch by dotted lines. These wicks are constructed in a peculiar way: first a cylinder of wire gauze is made and then woven lamp cotton is stretched over it so that when the wick is in its place, and attached to the rack or regulating wire, it can be raised and lowered and so far adjusted with facility and uniformity. The diameter of the ring of oxygen jet holes is 3½ Inches; that of the inner wick 2¾ Inches; and that of the outer wick 4 Inches. Both the oil and oxygen are fed by supply pipes proceeding from beneath upwards, as in the former lamps.

For the purpose of carrying away the soots, and smoke formed during the combustion of the lamp, I have had a small iron tube chimney placed over it. This is 4 Inches in diameter but it’s lower edge is full 9 Inches above the level of the wick of lamp; as high indeed as it could be to collect the soot and smoke; so that the draft on the flame was as small as possible and very little affected it’s form. It would be impossible in practice to burn the lamp without such a chimney; and in the present case it was not applied until after the first days experiments were concluded.

No glass cylinder has been used round the flame, the lamp being intended to burn without one.

I have made many careful experiments with this lamp for the purpose of ascertaining the light which it would give in a state approaching to it’s best condition and I have burnt it at different times with different proportions of oxygen and fuel, always endeavouring to obtain the best possible light.

Thus on one day, the average best light of many observations, was equal to 32.44 standard Argand lamps; the proportion of oil burnt, being equal to 14.4 pints in 12 hours, and of gas, consumed 216 cubic feet in the same time.

On a second day the average best light was equal to 20.777 standard Argand lamps; the proportion of oil being 14.06 pints, and of oxygen gas 164.53 cubic feet for twelve hours.

On a third day the average best light was equal to 19.8 Argand lamps; the proportion of oil being 9.9 pints, and of oxygen gas 144 cubic feet for 12 hours.

In the estimate of the expence of the lights given in the last Report (dated 15th January 1838³) the price of the oil was taken at 6s/10d per gallon, and that of the oxygen with the charge of fuel and retort expences upon it at 2.015 pence per cubic foot. Hence the whole cost on each of the three days above, would be,

But if we convert the cost into that which would have been incurred by the light equal to a single Argand lamp for 12 hours, then it will be,

for the first day 18 pence

second day 22.9

third day 19.77

This result enables us to compare it with the expence of the same quantity of light obtained from the former lamp of Mr. Gurney, and also from the French, and the common Argand lamp; for on turning to the former Report it will be found that such light obtained by

In it’s best condition therefore this lamp is much below the former lamp constructed by Mr. Gurney, and I think it not difficult to perceive the cause. The general condition of the flame is such as to occasion a contraction of it from it’s base upwards, in consequence of which, much oxygen, passing upright through the side of the flame, is left unconsumed and is lost;- and if more fuel be supplied for the purpose of catching the oxygen, then a great increase is made to the smoky part above, and so fuel is wasted. That this lamp wastes fuel far more than the former lamp is evident from the increased quantity of soots produced by it.

I now proceed to describe some other points regarding this lamp. It’s light changes very suddenly so as to fall sometimes almost one half, in a few minutes, and this arises from two principal causes. In the first place little cones of charcoal are apt to form round the oxygen jet holes, when the lamp is hot, and they very rapidly deteriorate the light and lower it’s force. In the next place the heat of the lamp is so great that the cotton is apt to char on the wire gauze cylinders, and so the supply of oil ceasing, more, or less, the light of course falls.

When however this is the case, and the lamp is hot, by raising the wire gauze a little, and giving a greater height to the oil by elevating the fountain head, the oil at the burner will go on boiling from the heat of the metal and supply fuel to the flame though there is little or no cotton in action. But that effect involves at present two or three new inconveniences. First the wire gauze is then, necessarily, so high that a very large proportion of those rays of light which ought to go in a direction downwards, are cut off by it;- and if for experiments sake the gauze be lowered, then the common air drawn by the flame, carries it inwards towards the central line so suddenly that much oxygen passes through the side of the flame, unused, and so the light falls. In the next place when the lamp is in this hot state the oil on the outside of the oil vessel, gradually chars on the metal, forming a wick there, and the lamp will be on fire burning nearly an inch downward on the outside of the burner. This not only wastes the oil but reddens the flame and causes the little charcoal cones to form round the oxygen jets in abundance. For this reason such charred oil must be cleared away.

The various liabilities of this lamp render it necessary that the attention given to it should be very constant and close, far more so indeed than with the former lamp; and even with such attention the light obtained from it for a certain expence does not, according to my results, nearly equal that given by the former lamp⁴.

I have the honor to be | My Lords & Gentlemen, | Your most obedient Servant | (signed) M. Faraday

Royal Institution | 14th June 1838.