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uninterruptedly on to the end of the bulb, you will suddenly see the black cross (c, d, Fig. 9B) change to a luminous one (e, f), because the background is only faintly phosphorescing, whilst the part which had the black shadow on it retains its full phosphorescent power. The luminous cross is now dying out. This is a most delicate and venturous experiment, and I am fortunate in having succeeded so well, for it is one that cannot be rehearsed. After resting for a time the glass seems to partly recover its power of phosphorescing, but it is never so good as it was at first.

We have, therefore, found an important fact connected with

this phosphorescence. Something is projected from the negative pole which has the power of hammering away at the glass in front of it, in such a way as to cause it not only to vibrate and become temporarily luminous while the discharge is going on, but to produce an impression upon the glass which is permanent. The explanation which has gradually evolved itself from this series of experiments is this:-The exhaustion in these tubes is so high that the dark space, as I showed you at the commencement of this lecture, that extended round the negative pole, has widened out till it entirely fills the tube. By great rarefaction the mean free path has become so long that the hits in a given

time may be disregarded in comparison to the misses, and the average molecule is now allowed to obey its own motions or laws without interference. The mean free path is in fact comparable to the dimensions of the vessel, and we have no longer to deal with a continuous portion of matter, as we should were the tubes less highly exhausted, but we must here contemplate the molecules individually. At first this was only a convenient working hypothesis. Long-continued experiment then raised this provisional hypothesis almost to the dignity of a theory, and now the general opinion is that this theory gives a fairly correct explanation of the facts. In these highly exhausted vessels the mean free path

sent me by Messrs. Hopkin and Williams; by ordinary light it is a perfectly white powder. It is just possible that the rich fire of the ruby, which has caused it to be so prized, may be due not entirely to the colouring-matter, but to its wonderful power of phosphorescing with a deep red colour, not only under the electric discharge in a vacuum, but when ever exposed to a strong light.

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The spectrum of the red light emitted by all these varieties of alumina--the ruby, corundum, or artificially precipitated alumina-is the same as described by Becquerel twenty years ago. There is one intense red line, a little below the fixed line B in the spectrum, having a wave-length of about 6895. There is a continuous spectrum beginning at about B, and a few fainter lines beyond it, but they are so faint in comparison with this red line that they may be neglected. This line may be called the characteristic line of alumina.

I now pass on to another fact connected with this negative discharge. Here is a tube (Fig. 12) with a negative pole (a, b) in the form of a hemi-cylinder, similar to the one you have already seen (Fig. 3), but in this case I receive the rays on a phosphorescent screen (c, d). See how brilliantly the lines of discharge shine out, and how intensely the focal point is illu minated; it lights the whole table. Now I bring a small magnet near, and move it to and fro; the rays obey the magnetic force, and the focus bends one way and the other as the magnet passes it. I can show this magnetic action a little more definitely. Here is a long glass tube (Fig. 13), very highly exhausted, with a negative pole at one end (a) and a long phosphorescent screen (b, c) down the centre of the tube. In front of the negative pole is a plate of mica (b, d) with a hole (e) in it,

a

FIG. 12.

the south pole twists it the cther way; the two poles side by side compel the ray to move in a straight line up or down, along a plane at right angles to the plane of the magnet and a line joining its poles.

Now it is of great interest to ascertain whether the law governing the magnetic deflection of the trajectory of the molecules is the same as has been found to hold good at a lower vacuum. The former experiment was with a very high vacuum. This is a tube with a low vacuum (Fig. 15). On passing the induction spark it passes as a narrow line of violet light joining the two poles. Underneath I have a powerful electro-magnet. I make contact with the magnet, and the line of light dips in the centre towards the magnet. I reverse the poles, and the line is driven up to the top of the tube. Notice the difference between the two phenomena. Here the action is temporary. The dip takes place under the magnetic influence; the line of discharge then rises, and pursues its path to the posi tive pole. In the high exhaustion, however, after the ray of light had dipped to the magnet it did not recover itself, but continued its path in the altered direction.

During these experiments another property of this molecular discharge has made itself very evident, although I have not yet drawn attention to it. The glass gets very warm where the green phosphorescence is strongest. The molecular focus on the tube, which we have just seen (Fig. 12) would be intensely hot, and I have prepared an apparatus by which this heat at the focus can be intensified and rendered visible to all present. This small tube (a) (Fig. 16) is furnished with a negative pole in the form of a cup (6). The rays will therefore be projected to a focus in the middle of the tube (Fig. 17, a). At the side of the tube is a small electro-magnet, which I can set in action by touching a key, and the focus is then drawn to the side of the glass tube (Fig. 17, 6). To show the first action of the heat I have coated the tube with wax. I will put the apparatus in front of the electric lantern (d), and throw a magnified image of the tube on the screen. The coil is now at work, and the focus of molecular rays is projected along the tube. I turn the magnetism on, and draw the focus on the side of the glass. The first thing you see

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The is a small circular patch melted in the coating of wax. glass soon begins to disintegrate, and cracks are shooting starwise from the centre of heat. The glass is softening. Now the atmospheric pressure forces it in, and now it melts. A hole (e) is perforated in the middle, the air rushes in, and the experiment is at an end.

Instead of drawing the focus to the side of the glass with a magnet, I will take another tube (Fig. 18), and allow the focus from the cup-shaped negative pole (a) to play on a piece of platinum wire (6) which is supported in the centre of the bulb. The platinum wire not only gets white-hot, but you can see sparks coming from it on all sides, showing that it is actually melting.

Here is another tube, but instead of platinum I have put in the focus that beautiful alloy of platinum and iridium which Mr. Matthey has brought to such perfection, and I think that I shall succeed in even melting that. I first turn on the induction-coil slightly, so as not to bring out its full power. The focus is now playing on the iridio-platinum, raising it to a white heat. I bring a small magnet near, and you see I can deflect the focus of heat just as I did the luminous focus in the other tube. By shifting the magnet I can drive the focus up and down, or draw it completely away from the metal, and render it non-luminous. I withdraw the magnet, and let the molecules have full play again; the metal is now white-hot. I increase the intensity of the spark. The metal glows with almost insupportable brilliancy, and at last melts.

There is still another property of this molecular discharge, and it is this:-You have seen that the molecules are driven

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the way the magnet is turned. I now throw the image of the apparatus on the screen. The spiral lines painted on the wheel show which way it turns. I arrange the magnet to draw the molecular stream so as to beat against the upper vanes, and the wheel_revolves rapidly, as if it were an over-shot water-wheel. I now turn the magnet so as to drive the molecular stream underneath; the wheel slackens speed, stops, and then begins to rotate the other way, as if it were an undershot water-wheel. This can be repeated as often as I like to reverse the position of the magnet, the change of rotation of the wheel showing immediately the way the molecular stream is deflected.

This experiment illustrates the last of the phenomena which time allows me to bring before you, attending the passage of the induction spark through a highly exhausted atmosphere. It will now be naturally asked, What have we learned from the phenomena described and exhibited, and from the explanations that have been proposed? We find in these phenomena confirmation of the modern views of matter and energy. The facts elicited are in harmony with the theory that matter is not continuous but composed of a prodigious number of minute particles, not in mutual contact. The facts also are in full accordance with the kinetic theory of gases-to which I have already referred-and with the conception of heat as a particular kind of

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energy, expressing itself as a rapid vibratory motion of the particles of matter. This alone would be a lesson of no small value. In science every law, every generalisation, however well established, must constantly be submitted to the ordeal of a comparison with newly-discovered phenomena; and a theory may be pronounced triumphant when it is found to harmonise with and to account for facts which, when it was propounded, were still unrecognised or unexplained.

But the experiments have shown us more than this: we have been enabled to contemplate matter in a condition hitherto unknown-in a fourth state-as far removed from that of gas as gas is from liquid, where the well-known properties of gases and elastic fluids almost disappear, whilst in their stead are revealed attributes previously masked and unsuspected. In this ultragaseous state of matter phenomena are perceived which in the mere gaseous condition are as impossible as in liquids or solids.

I admit that between the gaseous and the ultra-gaseous state there can be traced no sharp boundary; the one merges imperceptibly into the other. It is true also that we cannot see or handle matter in this novel phase. Nor can human or any other kind of organic life conceivable to us penetrate into regions where such ultra-gaseous matter may be supposed to exist. Nevertheless, we are able to observe it and experiment on it, legitimately arguing from the seen to the unseen.

Of the practical applications that may arise out of these researches, it would now be premature to speak. It is rarely given to the discoverer of new facts and new laws to witness their immediate utilisation. The ancients showed a perhaps unconscious sagacity when they selected the olive, one of the slowest growing trees, as the symbol of Minerva, the goddess of Arts and Industry. Nevertheless, I hold that all careful honest research will ultimately, even though in an indirect manner, draw after it, as Bacon said, "whole troops of practical applications."

NOTES

A MEETING of the Executive Committee having charge of the whole arrangements for the approaching visit of the British Association to Sheffield was held the other day. In connection with the Guide Book it was reported that contributions were arranged from Prof. Green, Mr. Arthur Jackson, Mr.. Trittain, Mr. G. R. Vine, Mr. J. D. Leader, and others. It is proposed to issue the guide books at Is. each, and they will contain scientific and other information suitable for visitors and residents. Dr. Sorby stated that a number of eminent men from foreign countries, including representatives from Germany, Italy, France, Belgium, the United States, and other parts of the world, had accepted invitations to take part in the meetings in Sheffield. These distinguished visitors will represent different branches of science; and from France the British Association is this year to be honoured, after the lapse of a long period, with the presence of the President of the Academy of Sciences, M. Daubrée. The Mayor (Ald. Ward) is to give a banquet to a number of distinguished guests in the banqueting hall of the Cutlers' Company on Saturday, August 23. A reception is to be given by the Master Cutler and Cutlers' Company, which will take place in the Cutlers' Hall on Thursday, August 21. A soirée is to be arranged by the local committee for the Tuesday following, also in the Cutlers' Hall. The arrangements for the excursions are being actively carried out. The Duke of Devonshire has invited a limited number of Members of the Association to a luncheon at Chatsworth. Earl Manners has invited a number of excur. sionists to luncheon at Thoresby, with the additional offer that they should be driven round the forest and park afterwards. Sir Joseph Whitworth has offered hospitality to a party of excursionists visiting Darley Dale and the district, and a similar offer has been made by Mr. F. C. Armitage, as regards a party exploring Arborlowe. The Rev. A. W. Hamilton-Gell invites a number of excursionists to Stanton-in-Peak, with the promise that they should see Router Rocks and other places of interest. Sir John Lubbock is to be asked to give an address at Arborlowe on the interesting Druidical remains there to be seen. Generally the arrangements were reported to be in a very satisfactory state.

SOME weeks since we stated that a committee had been

formed for the purpose of raising a fund for the benefit of the widow and family of the late Mr. W. G. Valentin, F.C.S. We understand that many of the friends and former pupils of this well-known chemist have responded with liberality, but as there may be others whom previous appeals have not reached, we have pleasure in stating that subscriptions will still be received by the hon. treasurer of the fund, Mr. F. W. Bayly, Royal Mint, E.

THE success which attended Mr. Tegetmeier's reprint of Boddaert's "Table des Planches Enluminées," and Mr. Dresser's reproduction of Eversmann's Addenda to Pallas's "Zoographia Rosso-Asiatica," has suggested the organisation of a "Willoughby Society for the Reprinting of scarce Ornithological Works," which has accordingly been formed, with every prospect

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of success.

The annual subscription is 17., and no copies of the works reprinted will be sold. The selection of the works to be reprinted by the Society has been intrusted to a committee consisting of the past and present editors of The Ibis, and Tunstall's 'Ornithologia Britannica" will be the first work reproduced. Particulars may be obtained from the secretary, F. D. Godman, Esq., 10, Chandos Street, Cavendish Square, W.

66

THE death is announced of Dr. Johann Karl Friedrich Rosenkranz, Professor of Philosophy at Koenigsberg University. Dr. Rosenkranz published a number of philosophical treatises, and was well known through his excellent edition of the works of Immanuel Kant. He died at the age of seventy-four on June 14.

THE monument of the late eminent botanist, Prof. Alexander Braun, was unveiled on June 17 at the Botanical Gardens of Berlin. The granite pedestal is by Prof. Adler, the bust of the deceased, which is said to be an excellent likeness, by the wellknown sculptor Prof. Schaper.

ACCORDING to the resolution passed at the last International Congress of Americanists at Luxemburg in 1877, the city of Brussels will be the meeting-place for this year's (third) congress. It will be held from September 23-26 under the protectorate of the King of the Belgians and the honorary presidency of the Count of Flanders. We have before stated the objects of the Congress, which will again be occupied by the consideration and discussion of a series of questions relating to the history, archæology, anthropology, ethnography, linguistics, and palæography

of North and South America.

the measurement of the velocity of projectiles; a cathetometer capable of measuring heights to the 1,200th of a millimetre, a new electric machine by induction, and a most efficient pneumatic machine, the invention of the eminent Padre Cecchi.

WE daresay most of our readers will be pleased at the result of the motion by Mr. S. Lloyd in the House of Commons, on Tuesday, in favour of appointing a Minister of Commerce and Agriculture. The motion was agreed to by a fair majority, among which were members of both sides of the House. This is a step in the right direction..

THE Giffard captive balloon has begun its series of night ascents by an experimental trip, which was made on June 30 with great success. The court of the Tuileries was lighted by ten Jablochkoff lamps. It is proposed to carry an electric lamp on the car if the sixty portable Bunsen elements which are in preparation can be carried without inconveniencing passengers. Captive ballooning is making its way in foreign lands. A captive balloon is being fitted up in one of the places of resort round New York; the balance for registering the levitation has been constructed in Philadelphia. It can register accurately 10,000 pounds, and is built for sustaining 25,oco.

PROF. VIRCHOw, Dr. Schliemann's companion and coadjutor in the latest excavations in the Troad, has written to the eminent Homeric archeologist, informing him of a concurrence of geological opinion at Berlin in the conclusion that all the building stones, fragments of which the professor brought home from Hissarlik, are of fresh-water formation. This conclusion is thought to be decisive against those who affirm the impossibility of identifying Hissarlik with the Homeric Troy, on the ground opened on the 24th inst. The preparations are being made with

that at the time of the great epic war the site must have been covered by the sea.

IN the Paris Academy of Sciences M. Dausse has been elected a Corresponding Member in the Section of Mechanics, in succession to the late General Didion.

THE French Minister of Fine Arts has placed at the disposition of the War Office fourteen cups of Sèvres china to be offered in competition to the societies of carrier-pigeon breeders.

THE Times Paris correspondent states that Dr. Krauss, at a scientific meeting at Stuttgart a few days ago, referred to the recent swarms of the Vanessa cardui butterfly. A like phenomenon occurred in Piedmont in 1741, 1826, and 1857. This year a swarm passed through Turin on June 2, through Switzerland from the 2nd to the 9th, Alsace, France, and Spain from the 5th to the 10th, and Würtemburg from the 11th to the 21st. Prof. Eimer, of Tübingen, found that eighteen out of nineteen specimens were females full of eggs, and he attributes the march to the search for a place to deposit their eggs; a march directed by their keen scent. Caterpillars have already been found on thistles in the districts visited, and a large number may be looked for.

THE thirty-sixth annual congress of the British Archæological Association is to be begun at Great Yarmouth on August 11, and continue until the 20th, the last three days, commencing on Monday, August 18, being passed at Norwich. Lord Waveney will deliver an inaugural address at the Town Hall, Great Yarmouth, as president of the meeting, on Monday, August 11, and the following days up to Saturday the 16th will be dedicated to a variety of interesting excursions.

IN connection with the celebration of the fiftieth anniversary of the Paris Central School of Arts and Manufactures, the Gazzetta d'Italia states that the meeting of engineers connected with the Florentine branch was held on Sunday, and that a banquet was given by the president, Commendatore Prof. Vegni. | After dinner those present visited the Workshop Galileo, in which so much is being done for the resuscitation of mechanical art in Florence, with no aid either from Government or the Municipality. Over the door of the workshop is a clock so ingeniously constructed that it has gone now for fourteen months with a loss of only five seconds. A chronograph was exhibited capable of registering the thousandth part of a second, and applicable to

THE Paris Exhibition of Sciences Applied to Industry will be

great activity in the Palais de l'Industrie. M. Jules Simon, the President of the Council, and M. Nicol, the Director, had an interview, on June 29, with the President of the Republic, to suggest a series of measures intended to promote the success of the exhibition.

MR. F. W. MOORE, eldest son of the late Dr. Moore, has been appointed Curator of the Botanic Gardens, Glasnevin, Dublin. Mr. Moore has been for some time curator of the College Botanic Garden, Dublin.

A SELECT Committee of the House of Commons, of which Mr. A. Pell was chairman, have concluded their consideration of the Bill promoted by the Liverpool Corporation, to give power to adopt and supply for public and private purposes lighting by electricity. The committee had intimated their decision to pass the Bill if amendments were made in the preamble, the effec. of which would be to limit the power of the Corporation to making a scientific experiment, and not allow them to make it a commercial undertaking for purposes of profit, or to compete with the gas company. Amendments were proposed by the Corporation in this direction, and the committee passed the Bill.

IT is stated that the Council of India, despairing of obtaining the repeatedly asked-for assistance of the Imperial Government towards defraying the cost of the India Museum, have decided to break it up and to distribute the collections between the British and South Kensington Museums and Kew.

FROM the report on the forests and plantations in the Island of Mauritius for 1878 we learn that many of the trees which were introduced from India a few years ago have thriven beyond expectation and have in some instances already reached the size of useful timber trees. Among those which have done best are mahogany, teak, and eucalyptus. The last named (E. calophyllus) is found to grow with remarkable vigour, and produces fertile seed at a very early age. The severe hurricanes which sweep over the island commit great devastation among the plan. tations of eucalyptus and other fast-growing trees, and the Government this season intend to plant out a large number of the young gum trees to be grown as large as bushes. In this form they are expected to be able to withstand the force of the wind, and form a screen for the protection of young plantations of timber trees.

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