In The Collected Letters of Erasmus Darwin, edited by Desmond King-Hele, Letter 86-6 from Erasmus Darwin to Josiah Wedgwood, 21 April 1786, starts off “Sir, Mr Nicholson is an ingenious and accurate man …” and continues a series of discussions between the men about oil lamp designs, leading to the comment that “The pyramidical lamp would be more pleasing to they eye than the concentric one of Mr Nicholson.”
Having been searching for Nicholson’s 'concentric lamp' for many years, I was delighted to finally track it down in The London Magazine, of May 1785:
Experiments and Observations Made with Argand’s PatentLamp.
As the attention of the world has been much excited by the powerful effects of Argand’s Lamp, and as there are many who are desirous of making use of it provided its advantages were clearly ascertained, I presume the following description of the instrument and its effects will not be unacceptable to the public.
The apparatus consists of two principal parts, a fountain to contain the oil, and the lamp itself. Of the former it is unnecessary to speak: the lamp is constructed as follows. The external parts consist of an upright metallic tube one inch and six-tenths in diameter, and three inches and a half in length, open at both ends. Within and concentric to this is fixed another tube of about one inch in diameter, and nearly of equal length; the space between these two tubes being left clear for the passage of air. The interior tube is closed at the bottom, and contains another similar tube a little more than half an inch in diameter. The third tube is soldered to the bottom of the second. It is perforated throughout so as to admit a current of air to pass through it, and the space between this tube and that which invirons it contains the oil. An ingenious apparatus, containing a piece of cotton cloth whose longitudinal threads are much the thickest, is adapted to nearly fill the space into which the oil flows. It is so contrived that the wick may be raised or depressed at pleasure. When the wick is considerably raised it is seen of a tubular form, and by the situation of the tubes already described is accessible to the air, both by means of the central perforation and the space between the exterior and second tube. When the wick is lighted, the flame is consequently in the form of a hollow cylinder, and is exceedingly brilliant. It is rendered somewhat more bright, and perfectly steady, by adapting a glass chimney whose dimensions are nearly the same with that of the exterior tube first described.
I hope this short description will be sufficient to convey an adequate idea of the instrument and shall therefore proceed to mention its effects. If the central hole be stopped, the flame changes from a cylindrical to a pyramidical form, becomes much less bright, and emits a considerable quantity of smoke. If the whole aperture be entirely or nearly stopped and the combustion becomes still more imperfect. The access of air to the external and internal surfaces of the flame is of so much importance, that a sensible difference is perceived when the hand or any other flat substance is held even at the distance of an inch from the lower aperture. There is a certain length of wick at which the effect of the lamp is the best. If the wick be too much depressed, the flame, though white and brilliant, is short; if it be raised, the flame becomes longer, and consequently the light more intense and vivid. A greater increase of the length, increases the quantity of the light, but at the same time the upper part of the flame assumes a brown hue, and smoke is emitted.
The lamp was filled with oil and weighed, it was then lighted and suffered to burn so as to produce the greatest quantity of light without smoke. After burning one hour and fifty-two minutes, it was extinguished and found to have lost 589 grains of its weight. Now a pint of oil weights 6520 grains and costs sixpence three farthings in retail; the lamp therefore consumes oil to the value of one penny in three hours. It remains to be shewn at what rate per hour the same quantity of light might be obtained from the tallow candles commonly used in families.
The candle called a middling fix, weighing upon an average the sixth part of a pound of avoirdupois, is 10¾ inches long, and 2 inches and 6/10 inch circumference. I have chosen to make my comparison with this candle as being, I imagine, most commonly used. It is to be understood that the lamp gave its maximum light without smoke.
The best method of comparing two lights with each other, that I know of, is this: Place the greater light at a considerable distance from a white paper, the less light may be moved nearer or father from the paper, accordingly as the experiment requires. If now an angular body, as the most convenient figure, be held before the paper it will project two shadows, these two shadows can coincide only in part, and their angular extremities will in all positions but one be at some distance from each other: the shadows being made to coincide in a certain part of their magnitude, they will be bordered with a lighter shadow, occasioned by the exclusion of the light from each of the two luminous bodies respectively. These lighter shadows in fact are spaces of the white paper illuminated by the different luminous bodies, and may with the greatest ease be compared together, because at a certain point they actually touch one another. If the space illuminated by the less light appear brightest, that light is to be removed farther off; and on the contrary, if it be the most obscure, that light must be brought nearer the paper. A considerable degree of precision may be obtained by this method of judging of lights, and by this method the following comparisons were made.
The candle was suffered to burn till it wanted snuffing so much, that large lumps of coaly matter were formed on the upper part of the wick. The candle then at the distance of 24 inches gave a light equal to that of the lamp at the distance of 129 inches: from this experiment it is deduced that the light of the lamp was equal to about 28 candles.
The candle was then snuffed, and it became necessary to remove it to the distance of 67 inches, before its light was so diminished as to equal that of the lamp at the before mentioned distance of 129 inches. From this experiment it is deduced that the light of the lamp was equal to not quitefour candles fresh snuffed.
Another trial with the lamp at the distance of 131 inches and a half, and another candle of the same size at the distance of 55 inches gave the lights equal. The candle was suffered to burn for some time, but did not seem to want snuffing, yet the light of the lamp then appeared to be stronger. The candle when newlysnuffed, the distances remaining the same, appeared rather to have the advantage of the lamp. These numbers give 5 2/3 candles for the light of the lamp, and I imagine the lamp to be rather better than this upon an average, because candles are suffered to go a much longer time without snuffing, and therefore in general give less lightthan was exhibited in these trials.
Another trial with the lamp raised so as to smoke a little, and the candle wanting snuffing, though the form of the wick had not yet begun to change, gave the proportion of the lamp to the candles at about 8 to 1. We may, therefore, I resume, take six middling fixes of tallow candles as an equivalent in light to the lamp. I tried the lamp against 4 candles lighted up together, placed on a distant table with the lamp, I retired till I could just discern the letters of a printed book by the light of the candles, the lamp being covered. I then directed my assistant to intercept the light of the candles and suffer the lamp to shine on the book; the lamp was the brightest. It seemed by trials of this kind to be rather better than five candles; but I was not at that time aware of the difference of the light of tallow candles, accordingly as they have been more or less recently snuffed, and as this method does not appear capable of that degree of exactness and facility the other possesses, I did not pursue it.
From these trials, it is evident that where light beyond a certain quantity is wanted, at a given place, these lamps must be highly advantageous; for the tallow candle being of six in a pound, and burning not quite seven hours, the lamp is equivalent to a pound of these candles lighted up for seven hours. Now, the expence of the lamp for seven hours is less than two pence halfpenny, and that of the candles eight pence; and if the proportion between wax and tallow candles be attended to, it will be seen that the advantages of this lamp for illuminating a theatre are very great.
The wax candles in Covent Garden Theatre are about eighty in number in the sconces, and by estimation may be worth about 2L sterling. An equal quantity of light would be afforded by fourteen of the patent lamps; for the candles used at the theatre do not give quite so much light as a tallow candle of six in a pound. The expence of the fourteen lamps for five hours will not exceed two shillings, according to the foregoing deduction.
Mr. Argand is certainly entitled to all the honour which his talents for philosophical combination have gained; and in the present instance, his claim as an inventor ought not to be disputed, though it should appear that the principle of his lamp was known and even applied to use long ago. Everyone is acquainted with the observation of Dr. Franklin, concerning the increase of light produced by joining the flames of two candles: and double candles have actually been made for, and used by shoemakers from time immemorial. The lamp of many wicks ranged in a right line, and used by watchmakers, gives a very great light for the same reason, namely because the flame being of no considerable thickness has access to air throughout and the combustion is perfectly maintained. Whereas in a thick flame the white heat or perfect ignition extends only to a certain distance from the exterior surface. This is exemplified in a striking manner in those large flames which issue from the chimnies of furnaces. These are luminous only to a certain distance inwards, and the interior part consists of vapour, hot indeed, but not on fire, so that If paper be held in the centre of the flame by means of an iron tube passed through the exterior burning part, the paper will not be set on fire. Mr. Argand has proposed the converting a right lined wick into a circular one; whether this be an advantage or no, except so far as concerns the convenience of having a longer range of conjoined flames within a less space I was desirous of ascertaining. The result of my trials are these.
I took one of Mr. Argand’s wicks, which when cut open longitudinally will form a line at the extremity proposed to be lighted, measuring about two inches and six-tenths. This wick was placed in a brass trough so that the upper edge of the wick was held perpendicular by the straight edge of the trough into which oil was put. The wick was then lighted, and it was easy to raise or lower it above the metallic edge at pleasure, because it adhered by means of the oil to the side of the brass vessel. I thus obtained a flame in a right line equal in length to the periphery of Argand’s flame, and as is the case in that lamp, I found it easy to lengthen or shorten the flame, to cause it to smoke or burn clear as has been before mentioned. The lamp and this right lined flame were placed near each other, and at the same height, the glass chimney being taken off the former: the flames of both were adjusted so as to emit a small quantity of smoke, and their lights tried. The experiment being made by means of the shadows, as before described, their lights proved exactlythe same: but to the eye, looking at both lamps together, the intensity of Argand’s flame appeared considerably the greatest; that is to say, it dazzled more and left a stronger impression when the organ of sight was directed to some other object.
Before I made this experiment I had some expectation, that the long flame would be preferable to the circular one, because I supposed the interior surface of the circular flame, could not throw out so much light as it would have done if it had been developed and exposed. I was even inclined to imagine that the greater part of the light of Argand’s lamp is furnished by the external surface of the flame. But the equality of the lights in the circular and the right-lined flames, shews that this opinion was ill founded, and that flame is in a very high degree transparent.
I therefore directed my attention to the shadow of a lighted candle, and observed, that when the candle does not smoke, the shadow is nearly the same as if the candle were not lighted; that is to say, as if there was no flame. But, if a piece of glass be held up in the same light, it will give a shadow sufficiently sensible: it therefore intercepts more of the light than flame does. This observation accounts for the superior brightness or dazzling of Argand’s lamp. For the light which falls on a given portion of the retina of the eye from Argand’s lamp is much more dense, because it consists not only of the light from the anterior but likewise from the posterior part of the flame.
My ideas on this subject were farther confirmed by an experiment I made with the two lamps; I placed the right-lined flame in such a direction that it should not, as it did before, shine on the paper by its broad side, but in the direction of its length; the comparison of its light with that of Argand’s lamp still exhibited equality. But the long flame was then much more dazzling and bright than that of Argand. This circumstance, which though highly curious, has not, as I know of, been before noticed, at least with that attention it deserves, may be applied to many valuable purposes; one in particular occurs to me that I cannot help mentioning. It should seem that anyproportion of light may be had for microscopic purposes, by means of a long flame placed in the direction of the axis of the illuminating lense.
I tried the transparency of this long flame, placed at right angles, to the ray of Argand’s lamp; it have no shadow; but when its length was placed in the direction of the ray, it gave a shadow bordered by two broad, well defined bright lines, which I have not yet sufficiently examined to be able to give any conjecture respecting them; thought they are undoubtedly owing to some optical deviation of the rays which pass in the vicinity or through the substance of the flame.
These observations on the transparency of flame suggest an improvement of which Argand’s lamp is susceptible. Instead of one ring of flame there may be two, three or more concentric rings, with air passages between them. The inner rings will shine through the outer with more facility than the presentflame does through the glass chimney; and it is probable that the rapidity of the current of air will be increased in a high proportion between these tubes of flame, so as to increase the vehemence and quantity of the ignition, and cause more light to be emitted than would answer to the mere increase of the line of wick.
P.S. Upon looking over this paper it occurred to me, that the singular fact of the same candle that gave only one twenty-eighth part of the light of the lamp, becoming so bright on being snuffed, as to give more than one fourth of the same light it was compared with (which is seven times as bright as before) might seem erroneous or founded in mistake. I have therefore, made several other experiments with snuffed and unsnuffed candles, and am well assured that a candle, newly snuffed, gives in general eight or even nine candles that have been suffered to burn undisturbed for an hour in a still place.
Just sorting out all the emails from after the Bloomsbury Festival event and found all these lovely compliments, which I cannot resist recording for posterity:
“a really enjoyable event and mixing in the young scientists worked really well. Well done to everyone involved!” Olivia
“I am so impressed with all the work that Diana, Sue and Ian put in as well as the actors and students. Brilliant!” Anita
“What a great event - I thought it was very moving seeing all those people standing listening and responding to the script. And if you’ve seen the David Attenborough documentary the PhD students are a shining beacon of hope that we might save humankind.” Ian.
“It really was a brilliant event, so well done to all! Jules and Sue struck just the right tone and it was so good having the students demonstrate the relevance tous today of Mr Nicholson's scientific endeavours. Great scripting, performances and direction, and flawless organisation and admin too (I know Diana and Sue put more time into this than you might guess). It was all impressive and generally wonderful.” Jo
“Ian, Sue and Jules - you were all excellent and clearly had worked very hard over many sessions to make the performance so polished, interesting, and amusing. You held the attention of that large audience and inclusion of the students was inspiring and they did their bit so well. Many thanks to you.” Sue
“What a fantastic event this afternoon! Everyone seemed to have a great time and I learnt a lot about William Nicholson and science. Huge congrats to Sue Bramall, the fabulous actor Jules Date and Ian Brown. Very well done.” Hans.
In case any the organisers of science or history events are looking for something a bit different – we’d love to do it again!
Can you shed light on
Mr Nicholson’s life?
Propose a guest blog
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