such a degree that it was impossible to try any experiments with it in such a place as London. A person stepping from one room to another altered the position of the centre of gravity of the house. If I walked from one side of my own laboratory to the other, I tilted the house over sufficiently to upset the equilibrium of the apparatus. Children playing in the streets disturbed it. Professor Rood, who has worked with an apparatus of this kind in America, finds that an elevation of its side equal to 600bt part of an inch is sufficient to be shown on the instrument. It was therefore out of the question to use an instrument of this construction, so I tried another form in which a fine glass beam, having discs of pith at each end, is suspended horizontally by a fine glass fibre, the whole being sealed up in glass and perfectly exhausted. To the centre of oscillation a glass mirror is attached.

Now a glass fibre has the property of always coming back to zero when it is twisted out of its position. It is almost, if not quite, a perfectly elastic body. I will show this by a simple experiment. This is a long glass fibre hanging vertically, and having a horizontal bar suspended on it. I hold the bar, and turn it half round; it swings backwards and forwards for a few times, but it quickly comes back to its original position. However much twist, however much torsion, may be put on this, it always returns ultimately to the same position. I have twisted glass fibres round, and kept them in a permanent state of twist more than a hundred complete revolutions, and they always came back accurately to zero. The principle of an instrument that I shall describe farther on depends entirely on this property of glass.

Instead of using silk to suspend the torsion beam with, I employ a fibre of glass, drawn out very fine before the blow-pipe. A thread of glass of less than the thousandth of an inch in thickness is wonderfully strong, of great stiffness, and of perfect elasticity, so that however much it is twisted round short of the breaking point, it untwists itself perfectly when liberated. The advantage of using glass fibres for suspending my beam is, therefore, that it always returns accurately to zero, after having tried an experiment, whilst I can get any desired amount of sensitiveness by drawing out the glass fibre sufficiently

fine.

Here, then, is the torsion apparatus sealed on to a Sprengel pump. It consists of a horizontal beam suspended by a glass fibre, and having discs of pith at each end coated with lampblack. The whole is enclosed in a glass case, made of tubes blown together, and by means of the pump the air is entirely removed. In the centre of the horizontal beam is a silvered mirror, and a ray from the electric light is reflected from it on to a scale in front, where it is visible as a small circular spot of light. It is evident that an angular movement of the torsion beam will cause the spot of light to move to the right or to the left along the scale. I will first show you the wonderful sensitiveness of the apparatus. I simply place my finger near the pith disc at one end, and the warmth is quite sufficient to drive the spot of light several inches along the scale. It has now returned to zero, and I place a candle near it. The spot of light flies off the scale. I now bring the candle near it alternately from one side to the other, and you see how perfectly it obeys the force of the candle. I think the movement is almost better seen without the screen than with it. The fog, which has been so great a detriment to every one else, is rather in my favour, for it shows the luminous index like a solid bar of light swaying to and fro across the room. The warmth of my finger or the radiation from a candle is therefore seen to drive the pith disc away. Here is a lump of ice, and on bringing it near one of the discs the luminous index promptly shows a movement of apparent

attraction.

With this apparatus I have tried many experiments, and amongst others I have endeavoured to answer the

question, "Is it light, or is it heat, that produces the movement?" for that is a question that is asked me by almost every one; and a good many appear to think that if the motion can be explained by an action of heat, all the novelty and the importance of the discovery vanishes. Now this question of light or heat is one I cannot answer, and I think that when I have explained the reason you will agree with me that it is unanswerable. There is no physical difference between light and heat. The spectrum, as scientific men understand it, extends from an indefinite distance beyond the red to an indefinite distance beyond the violet. We do not know how far it would extend one way or the other if no absorbing media were present; but, by what we may call a physiological accident, the human eye is sensitive to a portion of the spectrum situated between the line A in the red to about the line H in the violet. But this is not a physical difference between the luminous and non-luminous parts of the spectrum; it is only a physiological difference. Now, the part at the red end of the spectrum possesses, in the greatest degree, the property of causing the sensation of warmth, and of dilating the mercury in a thermometer, and of doing other things which are conveniently classed among the effects of heat; the centre part affects the eye, and is therefore called light; whilst the part at the other end of the spectrum has the greatest energy in producing chemical action. But it must not be forgotten that any ray of the spectrum, from whatever part it is selected, will produce all these physical actions in more or less degree. A ray here, at the letter C, for instance, in the orange, if concentrated on the bulb of a thermometer, will cause the mercury to dilate, and thus show the presence of heat; if concentrated on my hand I feel warmth; if I throw it on the face of a thermo-pile it will produce a current of electricity; if I throw it upon a sensitive photographic plate it will produce chemical actim; and if I throw it upon the instrument I have just described, it will produce motion. What, then, am I to call that ray? Is it light, heat. electricity, chemical action, or motion? It is neither. All these actions are inseparable attributes of the ray of that particular wave-length, and are not evidences of separate identities. I can no more split that ray up into five or six different rays, each having different properties, than I can split up the element iron, for instance, into other elements, one possessing the specific gravity of iron, another its magnetic properties, a third its chemical properties, a fourth its conducting power for heat, and so on. A ray of light of a definite refrangibility is one and indivisible, just as an element is, and these different properties of the ray are mere functions of that refrangibility, and inseparable from it. Therefore when I tell you that a ray in the ultra-red pushes the instrument with a force of 100, and a ray in the most luminous part has a dynamic value of about half that, it must be understood that the latter action is not due to heatrays, which accompany the luminous rays, but that the action is one purely due to the wave-length and the refrangibility of the ray employed. You now understand why it is that I cannot give a definite answer to the question, "Is it heat or is it light that produces these movements?" There is no physical difference between heat and light; so, to avoid confusion, I call the total bundle of rays which come from a candle or the sun, radiation.

I found, by throwing the pure rays of the spectrum one after the other upon this apparatus, that I could obtain a very definite answer to my first question, "What are the actual rays which cause this action?"

The apparatus was fitted up in a room specially devoted to it, and was protected on all sides, except where the rays of light had to pass, with cotton-wool and large bottles of water. A heliostat reflected a beam of sunlight in a constant direction, and it was received on an appropriate arrangement of slit, lenses, prisms, etc., for projecting a pure spectrum. Results were obtained in the months of July, August, and September; and they are represented graphically as a curve, the maximum

A comparison of these figures is a sufficient proof that the mechanical action of radiation is as much a function of the luminous rays as it is of the dark heat-rays. The second question, namely, "What influence has the colour of the surface on the action?" has also been solved by this apparatus.

In order to obtain comparative results between discs of pith coated with lampblack and with other substances, another torsion apparatus was constructed, in which six discs in vacuo could be exposed one after the other to a standard light. One disc always being lampblacked pith, the other discs could be changed so as to get comparisons of action. Calling the action of radiation from a candle on the lampblacked disc 100, the following are the proportions obtained ::

This table gives important information on many points; one more especially the action of radiation on lampblacked pith is five and a half times what it is on plain pith. A bar like those used in my first experiment, having one half black and one half white, exposed to a broad beam of radiation, will be pushed with five and a half times more strength on the black than on the white half, and if freely suspended will set at an angle greater or less according to the intensity of the radiation falling on it.

This suggests the employment of such a bar as a photometer, and I have accordingly made an instrument on this principle. It consists of a flat bar of pith, half black and half white, suspended horizontally in a bulb by means of a long silk fibre. A reflecting mirror and small magnet are fastened to the pith, and a controlling magnet is fastened outside, so that it can slip up and down the tube, and thus increase or diminish sensitiveness. The whole is completely exhausted and then enclosed in a box lined with black velvet, with apertures for the rays of light to pass in and out. A ray of light from a lamp reflected from the mirror to a graduated scale shows the movements of the pith bar.

The instrument fitted up for a photometric experiment is in front of me on the table. A beam from the electric light falls on the little mirror, and is thence reflected back to the screen, where it forms a spot of light, the displacement of which to the right or the left shows the movement of the pith bar. One end of the bar is blacked on each side, the other end being left plain. I have two candles, each twelve inches off the pith bar, one on each side of it. When I remove the screens the candle on one side will give the pith a push in one direction, and

the candle on the other side will give the pith a push in the opposite direction, and as they are the same distance off they will neutralize each other, and the spot of light will not move. I now take the two screens away; each candle is pushing the pith equally in opposite directions, and the luminous index remains at zero. When, however, I cut one candle off, the candle on the opposite side exerts its full influence, and the index flies to one end of the scale. I cut the other one off and obscure the first, and I obscure them the spot of light flies to the other side. both, and the index comes quickly to zero. I remove the screens simultaneously, and the index does not move.

I will retain one candle 12 inches off, and put two candles on the other side 17 inches off. On removing the screens you see the index does not move from zero. Now the square of 12 is 144, and the square of 17 is 289. Twice 144 is 288. The light of these candles, therefore, is as 288 to 289. They therefore balance each other as nearly as possible. Similarly I can balance a gas-light against a candle. I have a small gas-burner here, which I place 28 inches off on one side, and you see it balances the candle 12 inches off. These experiments show how conveniently and accurately this instrument can be used as a photometer. By balancing a standard candle on one side against any source of light on the other, the value of the latter in terms of a candle is readily shown; thus in the last experiment the standard candle 12 inches off is balanced by a gas-flame 28 inches off. The lights are therefore in the proportion of 12, to 282, or as 1 to 5.4. The gas-burner is therefore equal to about 5 candles.

In practical work on photometry it is often required to ascertain the value of gas. Gas is spoken of commercially as of so many candle-power. There is a certain "standard" candle which is supposed to be made invariable by Act of Parliament. I have worked a great deal with these standard candles, and I find them to be among the most variable things in the world. They never burn with the same luminosity from one hour to the other, and no two candles are alike. I can now, however, easily get over this difficulty. I place a "standard" candle at such a distance from the apparatus that it gives a deflection of 100 degrees on the scale. If it is poorer than the standard I bring it nearer; if better, I put it farther off. Indeed, any candle may be taken; and if it be placed at such a distance from the apparatus that it will give a uniform deflection, say of 100 divisions, the standard can be reproduced at any subsequent time; and the burning of the candle may be tested during the photometric experiments by taking the deflection it causes from time to time, and altering its distance, if needed, to keep the deflection at 100 divisions. The gas-light to be tested is placed at such a distance on the opposite side of the pith bar that it exactly balances the candle. Then, by squaring the distances, I get the exact proportion between the gas and the candle.

Before this instrument can be used as a photometer or light measurer, means must be taken to cut off from it all those rays coming from the candle or gas which are not actually luminous. A reference to the spectrum diagram will show that at each end of the coloured rays there is a large space inactive, as far as the eye is concerned, but active in respect to the production of motion-strongly so at the red end, less strong at the violet end. Before the instrument can be used to measure luminosity, these rays must be cut off. We buy gas for the light that it gives, not for the heat it evolves on burning, and it would therefore never do to measure the heat and pay for it as light.

It has been found that a clear plate of alum, whilst letting all the light through, is almost, if not quite, opaque to the heating rays below the red. A solution of alum in water is almost as effective as a crystal of alum; if, therefore, I place in front of the instrument glass cells containing an aqueous solution of alum, the dark heat-rays are filtered off.

But the ultra-violet rays still pass through, and to cut these off I dissolve in the alum solution a quantity of

sulphate of quinine. This body has the property of cutting ff the ultra-violet rays from a point between the lines G ad H. A combination of alum and sulphate of quinine, terefore, limits the action to those rays which affect the human eye, and the instrument, such as you see it before yo, becomes a true photometer.

'his instrument, when its sensitiveness is not deadened by the powerful control magnet I am obliged to keep heart for these experiments, is wonderfully sensible to light. In my own laboratory a candle 26 feet off produces a decided movement, and the motion of the index increases inversely with the square of the distance, thus answering the third question, "Is the amount of action in direct proportion to the amount of radiation ?"

The experimental observations and the numbers which are required by the theoretical diminution of light with the square of the distance are sufficiently close, as the following igures show:

Candle 6 feet off gives a deflection of 218-0°

The effect of two candles side by side is practically double, and of three candles three times that of one candle.

In the instrument just described the candle acts on a pith bar, one end of which is blacked on each side. But suppose I black the bar on alternate halves and place a light near it sufficiently strong to drive the bar half round. The light will now have presented to it another black surface in the same position as the first, and the bar will be again driven in the same direction half round. This action will be again repeated, the differential action of the light on the black and white surfaces keeps the bar moving, and the result will be rotation.

Here is such a pith bar, blacked on alternate sides, and suspended in an exhausted glass bulb. I project its image on the screen, and the strong light which shines on it sets it rotating with considerable velocity. Now it is slackening speed, and now it has stopped altogether. The bar is supported on a fibre of silk, which has twisted round till the rotation is stopped by the accumulated tor sion. I put a water screen between the bar and the electric light to cut off some of the active rays, and the silk untwists, turning the bar in the opposite direction. I now remove the water, and the bar revolves rapidly as

at first.

From suspending the pith on a silk fibre to balancing it on a point the transition is slight; the interfering action of torsion is thereby removed, and the instrument rotates continuously under the influence of radiation. Many of these little pieces of apparatus, to which I have given the name of radiometers, are on the table, revolving with more or less speed. The construction is very simple. They are formed of four arms of very fine glass, supported in the centre by a needle-point, and having at the extremities thin discs of pith lamp-blacked on one side, the black surfaces all facing the same way. The needle stands in a glass cup, and the arms and discs are delicately balanced so as to revolve with the slighest impetus.

Here are some rotating by the light of a candle. This one now is rather an historical instrument, being the first one in which I saw rotation. It goes very slowly in comparison with the others, but it is not so bad for the first instrument of the sort that was ever made.

I will now, by means of a vertical lantern, throw on the screen the projection of one of these instruments, so as to show the movement rather better than you could see it on the table. The electric light falling vertically downwards on it, and much of the power being cut of by water and alum screens, the rotation is slow. I bring a candle near and the speed increases. I now lift the

radiometer up, and place it full in the electric light, projecting its image direct on the screen, and it goes so rapidly that if I had not cut out the four pieces of pith of different shapes you would have been unable to follow the movement. (To be continued.)

Parliamentary and Law Proceedings.

IMPORTANT TO DRUG GRINDERS. CONVICTION UNDER THE SALE OF FOOD AND DRUGS ACT.

A special petty session was held at Dunster on Friday, June 23rd, for the purpose of hearing an adjourned case, in which Mr. William Burnell, general shopkeeper, of Wootton Courtney, was summoned by Mr. Durham, inspector of weights and measures, for selling one ounce of adulterated pepper on the 25th of April. Mr. Cooper, wholesale druggist and chemist, of Exeter, by whom the article was supplied to the defendant, was in attendance and conducted the case for the defence.

Mr. Durham stated that on the 25th of April he purchased an ounce of pepper at the defendant's shop and took it, with other samples of various articles, to Mr. Stoddart, the county analyst, at Bristol, on the following day. He had received a certificate from Mr. Stoddart stating that the pepper was adulterated with ten per

cent. of starch.

Mr. W. W. Stoddart said he analysed the pepper in question and found that it contained at least ten per cent. of starch from the flour of beans or peas. He produced in a glass the starch which he had extracted from thirty grains of the pepper. He had since received a sample of pepper direct from the defendant for analysis, and had found that it also contained the same proportion of starch. In answer to Mr. Cooper the witness said the glass produced also contained some pure pepper starch. If some beans had been ground in a mill and pepper corns had afterwards been ground with the same stones, particular care not having been taken to cleanse the stones, it was quite probable that some of the bean flour would become mixed with the pepper accidentally. It might not affect the whole of the bulk of the pepper in the same proportion, but the first portion would be most affected. He thought it would pay a manufacturer to adulterate pepper with ten per cent. of starch. He had known Mr. Cooper for a great number of years, and did not think him capable of practising adulteration.

For the defence Mr. Burnell stated that he added nothing whatever to the pepper and that he sent a sample of it, by Mr. Cooper's request, to Professor Attfield of London.

Walter Frost, assistant to Mr. Cooper, of Exeter, proved sending seven pounds of pepper to the defendant about the last week in February. He received it in a ground state from Mr. Tapscott, a wholesale grocer. He had been with Mr. Cooper for sixteen years, and had not during that time known of any article being adulterated by Mr. Cooper or by his instructions. Nothing could be adulterated in his master's place without his (witness's) knowledge.

James Keen, assistant to Mr. Tapscott, wholesale grocer, of Exeter, produced a receiving book which was used for checking goods inwards and outwards, and in it was an entry in the handwriting of a commercial traveller of Mr. Tapscott, implying that two bags of whole white pepper were sent to the Round Tree Mill, Exeter, to be ground, on February 25th. He (witness) received the pepper after it had been ground on March 4th, and one of the bags he sent to Mr. Cooper about two hours afterwards. Nothing was added to it, to his knowledge, while it was in his possession, and nothing could have been added without his being aware of it. He had not known Mr. Tapscott adulterate anything during the time he had been in his employ.

nt sell fermented liquor. He contended that this was the only article known by the name of ginger ale, and tha therefore no fraud was attempted by selling it under thatname. He further argued that the name ginger ale was as correct as applied to this article as ginger beer was when applied to the article sold under that name. It was not sold to the prejudice of the purchaser, being of the substance, nature, and quality demanded by him, and there was nothing injurious to health in it.

Henry Cochrane, managing partner of the firm of Cantrell and Cochrane, said his firm had manufactured the ginger ale for the last twenty-five years along with other aerated waters, and it was sold very extensively. It was made from ginger, essence of lemon, capsicum, and other ingredients.

Mr. Hodgson, the defendant, said that the bottles sold by him to Mr. Booker were taken from his general stock. He had had other bottles analysed.

Dr. Terry, Bradford, gave evidence as to the wholesomeness of the ginger ale which he kept in his house. He sometimes used it medicinally, the capsicum having a good effect in neutralizing the results of ale drinking.

Mr. Thos. Fairley, public analyst, of Leeds, said he had analysed a sample of the ginger ale, and found nothing injurious to health in it. He found a trace of capsicum and ginger in it.

Dr. C. A. Burghardt, lecturer in mineralogy, and mineralogical chemistry at Owens College, Manchester,

corroborated.

The Bench, after a short consultation, dismissed the case.-Bradford Chronicle.

DEATH FROM CHLORAL HYDRATE.

The

Dr. Hardwicke, coroner for Central Middlesex, held an inquiry on the 13th ult. at the Queen's Arms, Haverstock Hill, concerning the death of Adrian Byron Ashford, aged 45, a gentleman of independent means. evidence of the widow, showed that deceased had suffered from liver complaint for some years. He had been in the habit of taking almost every evening a night-draught, which was supplied by a local chemist from a special prescription, in order to procure sleep. Mr. John West, residing in the same house, said he was called to deceased's bedroom at three o'clock on Friday morning where he found deceased lying on the floor, snoring very loudly. He soon after died. Mr. William Kerr, M.R.C.S., said chloral hydrate would greatly increase the narcotic effects of the stimulants deceased had been accustomed to take on retiring to bed. The cause of death was syncope, or failure of the heart's action whilst under the influence of an overdose of chloral hydrate. The jury unanimously agreed to a verdict of death from misadventure.--Echo.

ALLEGED ADULTERATION OF SOLUBLE COCOA LABELLED AS AN "ADMIXTURE."

The following important correspondence has taken place with reference to summonses which were heard before the Southampton County Bench of magistrates on the 26th May last:

The National Chamber of Trade, 446, Strand, W.C. 8th June, 1876. Sir,-I am requested by the Committee of the National Chamber of Trade to most respectfully direct your attention to the following extract from the Grocer of the 3rd inst., which appears to them to be of an extraordinary character, as the report states "that the cocoa was labelled as a compound.”

"Mr. Samuel Read, of Millbrook, and Mr. David Kerley, of West End, grocers, were summoned before the magistrates, on Friday, the 26th ult., for selling cocoa containing cocoa-butter, cane sugar, and sago-starch. The fact was proved that the cocoa was labelled as a com

pound. The Bench, notwithstan ling, decided that the defendants had made themselves liable for not stating this to the purchaser when the sale was effected. Fined 10s. 6d. each, and costs.

"Mr. Read said he thought they must give up selling cocoa should the conviction be confirmed. The magistrates intimated that it was a matter for the defendants to fight out with Messrs. Taylor Brothers, the manufacturers. The cocoa was one of the cheapest kind."

They have been favoured by the manufacturers with a copy of the label which is used upon the article for which the defendants in the above cases were convicted, a sample of which is appended.

(COPY OF REPLY FROM THE GOVERNMENT.,
No. 380236.
1876.

Local Government Board, Whitehall, S. W.
19th June, 1876.

SIR,-I am directed by the Local Government Board to acknowledge the receipt of your letter of the 8th instant, in which, at the request of the National Chamber of Trade, you call the Board's attention to a decision recently given by a bench of magistrates under the Sale of Food and Drugs Act, 1875.

The Board desire me to state that they have no authority to review the decision of the magistrates to which you refer, nor can any opinion of theirs settle the This can only be done by a decision of the High Court of Justice.

law in the case.

The Board has no information as to the grounds on which the decision of the magistrates was based, but they think that the label, of which you have forwarded a copy, might be framed in more distinct terms.

The Statute 38 and 39 Vic. cap. 63, sec. 8, requires that the vendor of any compound article of food shall supply to the person receiving it a notice "by a label distinctly and legibly written or printed on, or with the article, to the effect that the same is mixed.

In this particular case, for example, such words as the following might be used on the label: "This is an admixture, but contains no ingredient injurious to health." I am, Sir,