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summer left the Institution, our chemical laboratory was probably the very worst in London."

The physical laboratory remained unchanged; and although Professor Tyndall for himself desired nothing more than to continue his researches in a place which his imagination filled with the recollections of his predecessors, he still acquiesced in the proposal for rebuilding, for the sake of his successors, and in the interest of the sister science of his colleague.

Thus much about the material fabric of our laboratories. Next as to the scientific work of which they have been the birthplace.

Of the great names connected with this building foremost in order of time, and very high in scientific rank, stands that of Dr. Thomas Young. His "Theory of Light and Colours" will always stamp him as one "whose genius has anticipated the progress of science," and whose reputation has risen as men have better understood his worth. His first paper on the subject was presented to the Royal Society in November, 1801; but the earliest printed account of his views is to be found in his "Syllabus of Lectures at the Royal Institution," dated January 19, 1802. With the criticisms of his theory published in the Edinburgh Review, with the circumstances which led to his withdrawal from the Institution, with his researches in Egyptian hieroglyphics, we are not here concerned. But it is not too much to say of him, that without the Wave Theory of Light (of which he was one of the prime and main founders) to serve as a guiding-thread through the labyrinth of phenomena, the long series of discoveries which have in this place culminated in those of Tyndall in Radiation and Absorption, would have been impossible.

It is often remarked that little rills, which have threaded their way from distant mountains, ultimately discharge themselves as mighty streams into the sea. Yet between these two stages they flow quietly, but not therefore less usefully, past smiling meadows and the haunts of men, And here is a little scientific pastoral-if it may be so called-flowing out of the highest conceptions of the theory of undulations, and furnishing, to use his own words-a simple instrument "for measuring the diameters of the fibres of different kinds of wool."* [The lecturer then described and exhibited on the screen the principle of Dr. Young's eriometer.]

Our next name is that of Davy, an account of whose discoveries would require a volume, and a bare recital of them would be long. I quote the following notes from the pen of our Secretary, and wish that he had been here to give life to the dry bones.

In 1806, when twenty-eight years of age, Davy did the work which formed his first Bakerian Lecture, "On the Chemical Agencies of Electricity." Six years previously he had written, "Galvanism I have found, by numerous experiments, to be a process purely chemical." In the interim, water had been decomposed by electricity, and Davy began his researches with an inquiry into the changes produced in water by electricity. His main conclusion was that "the kind of polarity of each element determined the electrical and chemical actions shown by it." The French Academy awarded him a medal for this work; and from these discoveries the fame of our laboratories took its rise.

The next year Davy began a new series of experiments on Polarity. He exposed different substances to the action of platinum wires coming from a battery of 100 cells; and on October 6 he wrote in his note-book, "Remarkable phenomena with potash." On the 19th he made the following entry, "A capital experiment proving the decomposition of potash." He worked at the decomposition of other alkalies until the 23rd No

*The King at this time had his flock of merino sheep, and Sir Joseph Banks had the care of them at Kew. On his recovery from his first mental attack the King would only call the P.R.S. his woolstapler.

vember, when he was attacked by a fever which proved nearly fatal to him.

The importance of these decompositions to the recent science of spectral analysis, although not dreamt of at the time, can hardly be overrated; and I will therefore venture to interrupt my narrative for a moment by an experiment,-a very well-known one, which will serve to illustrate the point. [The speaker then exhibited the dark absorption line of sodium; but so arranged as to show the dark line in the centre of, and not entirely obliterating, the bright line; proving that a certain density of vapour is necessary for complete absorption.]

In 1808 he began to work on the composition of muriatic acid; and with a new battery provided for him by subscription, he attacked different substances with increased energy. In 1810 he sent to the Royal Society his researches on oxymuriatic acid and the elements of muriatic acid, on what is in fact now known as chlorine.

In 1811 he made the acquaintance of Mrs. Appreece, and in 1812 wrote to his brother, " In a few weeks I shall be able to return to my habits of study and research. I am going to be married to-morrow, and have a fair prospect of happiness with the most amiable and intellectual woman I have ever known." The issue of these hopes has been written by his biographers; but the disappointment of the last seventeen years of his life is illuminated by the invention, not less original in its conception than benevolent in its object, of the Safety Lamp.

The great value of this contrivance, and of questions arising out of it, will I trust, be sufficient apology for diverging again from my story in order to mention some very important experiments now in progress by Mr. Galloway. Explosions, it is well known, occur even in cases where the safety lamp is used. And it has been noticed that in these cases they occur most frequently after the firing of a blasting shot in the neighbourhood; and as it was almost certain that the penetration of the fire-damp through the gauze of the lamp was not due to a sudden flow of gas from one part of the mine to another, experiments have been instituted to determine whether the transmission of the sound wave, or wave of compression, may not have been the means of producing the mischief. Through the kindness of Mr. Galloway we have here a tube arranged for making such an experiment. At one end there is the inflammable current burning outside a safety lamp; in the centre is an elastic diaphragm, and at the other end a pistol will be fired, by the explosion of which a sound wave will be propagated along the tube. On the arrival of the sound wave at the extremity of the tube, the combustion will penetrate the safety lamp. But I here leave the matter in the hands of Mr. Galloway, of whose experiments we hope to hear more hereafter.

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(To be continued.)

PROFESSOR TYNDALL IN AMERICA HAT would the readers of any of our daily papers think, if they found half-a-dozen of its columns for six days on end, filled with verbatim reports of scientific lectures? Would not they be inclined to think their paper was in its dotage? But this has been done in the case of the New York Tribune, in whose columns, day after day, have appeared verbatim reports, with illustrations, of the six lectures which Prof. Tyndall delivered on Light in New York during the last days of last year? Not only has this been done, but the whole series of lectures has been issued on a separate sheet of four pages, each page as large as that of any of our daily papers, with twenty illustrations somewhat rude no doubt, but quite intelligible. This valuable sheet is sold at the astounding price of three cents, and as it has not a single advertisement, it must

Is not

have an immense circulation to be remunerative. this one among many signs that the untrammelled Americans are rapidly outstripping us in the love for and the spread of scientific knowledge? It is certainly a noteworthy phenomenon which we wish could be witnessed nearer home. The editorial preface to the series concludes thus :—“ If in the ulterior object of his (Professor Tyndall's) labours, the awakening of a spirit of scientific inquiry among our young thinkers, and the fostering of this tendency by liberal endowments from our wealthier citizens, his success shall be ultimately apparent, our whole country will have reason to thank the eminent Englishman." The following are a few passages from his concluding lecture :

"It is never to be forgotten that not one of those great investigators, from Aristotle down to Stokes and Kirchhoff, had any practical end in view, according to the ordinary definition of the word 'practical.' They did not propose to themselves money as an end, and knowledge as a means of obtaining it. For the most part, they nobly reversed this process, made knowledge of their end, and such money as they possessed the means of obtaining it. We may see to-day the issues of their work in a thousand practical forms, and this may be thought sufficient to justify it, if not ennoble their efforts. But they did not work for such issues; their reward was of a totally different kind. In what way different? We love clothes, we love food, we love fine equipages, we love money, and any man who can point to these as the results of his efforts in life justifies these efforts before all the world. In America and England more especially he is a practical man. But I would appeal confidently to this assembly whether such things exhaust the demands of human nature? Given clothes, given food, given carriages, given money is there no pleasure beyond what these can cover which the possessor of them would still covet? The very presence here for six inclement nights of this audience, embodying, I am told, to a great extent, the mental force and refinement of this city, is an answer to my question. I need not tell such an assembly that there are joys of the intellect as well as joys of the body, or that these pleasures of the spirit constituted the reward of our great investigators. Led on by the whisperings of natural truth, through pain and self-denial, they often pursued their work. With the ruling passion strong in death, some of them, when no longer able to hold a pen, dictated to their friends the results of their labours, and then rested from them for ever. . . . That scientific discovery may put not only dollars into the pockets of individuals, but millions into the exchequers of nations, the history of science amply proves; but the hope of its doing so is not the motive power of the investigator. It never can be his motive power.

"When analysed, what are industrial America and industrial England? If you can tolerate freedom of speech on my part, I will answer this question by an illustration. Strip a strong arm, and regard the knotted muscles when the hand is clinched and the arm bent. Is this exhibition of energy the work of the muscle alone? By no means. The muscle is the channel of an influence, without which it would be as powerless as a lump of plastic dough. It is the delicate unseen nerve that unlocks the power of the muscle. And without those fitaments of genius which have been shot like nerves through the body of society by the original discoverers, indust America and industrial England would, I fear, be very much in the condition of that plastic dough. At the present time there is a cry in England for technical education, and it is the expression of a true national want; but there is no outcry for original investigation. Still without this, as surely as the stream dwindles when the spring dries, so surely will their technica! education lose au force of growth, all power of reproduction. Our great investigators have given us sufficient work for a time;

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but if their spirit die out, we shall find ourselves eventually in the condition of those Chinese mentioned by De Tocqueville, who, having forgotten the scientific origin of what they did, were at length compelled to copy without variation the inventions of an ancestry who, wiser than themselves, had drawn their inspiration direct from Nature.

"To keep society as regards science in healthy play, three classes of workers are necessary: Firstly, the investigator of natural truth, whose vocation it is to pursue that truth, and extend the field of discovery for the truth's own sake, and without any reference to practical ends. Secondly, the teacher of natural truth, whose vocation it is to give public diffusion to the knowledge already won by the discoverer. Thirdly, the applier of natural truth, whose vocation it is to make scientific knowledge available for the needs, comforts, and luxuries of life. These three classes ought to coexist, and interact upon each other. Now, the popular notion of science, both in this country and in England, often relates, not to science strictly so called, but to the applications of science. Such applications, especially on this continent, are so astounding-they spread themselves so largely and umbrageously before the public eye-as to shut out from view those workers who are engaged in the profounder business of discovery."

After quoting De Tocqueville on the supposed unfavourable influence which republicanism has on the advance of science, Prof. Tyndall says :—

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"It rests with you to prove whether these things are necessarily so, whether the highest scientific genius cannot find in the midst of you a tranquil home. should be loth to gainsay so keen an observer and so profound a critical writer, but, since my arrival in this country, I have been unable to see anything in the constitution of society to prevent any student with the root of the matter in him from bestowing the most steadfast devotion on pure science. If great scientific results are not achieved in America, it is not to the small agitations of society that I should be disposed to ascribe the defect, but to the fact that men among you who possess the genius for scientific inquiry are laden with duties of administration or tuition so heavy as to be utterly incompatible with the continuous or tranquil meditation which original investigation demands. I do not think this state of things likely to last. I have seen in America willingness on the part of individuals to devote their fortunes in the matter of education to the service of the commonwealth, for which I cannot find a parallel elsewhere.

"This willingness of private men to devote fortunes to public purposes requires but wise direction to enable you to render null and void the prediction of De Tocqueville. Your most difficult problem will be not to build institutions, but to make men; not to form the body, but to find the spiritual embers which shall kindle within that body a living soul. You have scientific genius among you; not sown broadcast, believe me, but still scattered here and there. Take all unnecessary impediments out of its way. You have asked me to give these lectures, and I cannot turn them to better account than by asking you in turn to remember that the lecturer is usually the distributor of intellectual wealth amassed by better men. It is not as lecturers, but as discoverers, that you ought to employ your highest men. Keep your sympathetic eye upon the originator of knowledge. Give him the freedon necessary for his researches, not overloading him either with the duties of tution or of administration, not demanding from him so-called practical results above all things, avoiding that question which ignorance so often addresses to genius:What is the ue of your work?' Let him make truth his object, however impracticable for the time being, that truth my appear. It you cast your bread thus upon the waters, then be assured it will return to you, though it may be after many days."

ON THE SPECTROSCOPE AND ITS
APPLICATIONS

III.

So far, I have spoken of spectroscopes as spectroscopes -as one of the instruments the improvement of which should be cared for by every student in science. Their applications will come after. As may be imagined, spectroscopes are now constructed with one, two, three, four, or more prisms, the number depending on the pur

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pose for which they are to be employed.
ment with one prism is usually called a chemical spec-
troscope, for an instrument of this kind is now almost as
important and essential in a chemical laboratory as a
balance. Spectroscopes are also constructed with two
prisms, as shown in Fig. 13; these are used in cases when
rather more dispersion is desired than can be obtained
with the one-prism instrument. When, however, any
accurate and elaborate work has to be done, such as in
carrying out original investigations, more prisms have to

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FIG. 14.-Steinheil's form of four-prism spectroscope; arrangement of slit shown separately. why spectroscopes of many more prisms should not be employed, except that they require to be worked only with strong lights, as light is here so much dispersed or spread out that a feeble spectrum would be almost lost. As the principle of construction is almost the same in all kinds of spectroscopes, we had better commence by a description of the simplest form, namely, that with one prism, as shown in Fig. 15. It will be seen to consist of a circular table, supported by a pillar and three legs, carrying three lateral tubes; the right-hand tube is called the collimator, and holds at its outer extremity the fine

slit, the width of which can be regulated to a nicety by a micrometer screw; the other end of the collimator is furnished with a lens, which serves to collect the rays of light coming from the slit, and to render them parallel before falling on the prism in the centre of the table. The prism is so placed and fixed by a clamp that the light entering the slit from the source of light, shown in the figure as a gas lamp, strikes it and leaves it at what is called the angle of minimum deviation, a term which has already been explained; after passing through the prism, in which the light undergoes both deviation and dis

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objects, such as the sun and stars, comets, nebulæ, planets, and so on; we must for this purpose have something attached to the telescope. Fig. 16 shows a star spectroscope, which differs in arrangement only and not in principle from other spectroscopes, except in one point to which I have to draw attention with regard to this spectroscope. I have insisted on the importance of the slit; but you will see in a moment that the image of a star, if it is a good image, will be a mere point in the telescope, and therefore, while

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FIG. 17.-Direct-vision prism with three prisms.

a slit is not absolutely necessary, it is essential to have some arrangement by which that point of light, the spectrum of which would be merely a line, and therefore not broad enough to enable us to see what the lines are which we may expect in the spectra of stars, if they be anything like the spectrum of the sun, shall be turned into a band. That has been accomplished by means of a

cylindrical lens, its function being to leave the light alone in one direction, but to turn it into a band in another direction, so that when the light of the star gets through such a lens, it is no longer a point but a line, and this is then grasped by the collimating lens, sent through the prisms, and received by the observing telescope, so that when you get the image of it in the observing telescope, instead of having a line of light so fine that the lines in it cannot be distinguished, it is a distinctly broad band in which the lines can be observed. As this lens is simply a contrivance for enabling the eye to see about where there is a line, I submit now, as I submitted some years ago, that a proper place for it is close to the eye, between the eye and the image. I have been gratified to find that, in many of the spectroscopes used on the Continent, this arrangement is adopted.

We have now an idea of the action of the simple prism. I will next bring to your notice another kind of prism, which differs from the simple one very much as the achromatic telescope differs from the non-achromatic one, which was the first attempt made at an instrument for astronomical observations. Many of you know that the object-glass of a telescope, as now constructed, consists of two lenses made of different kinds of glass. Of course, we have dispersion and deviation at work in both these kinds of glass, but the lenses are so arranged, and their curves are so chosen, that, as a total result, the deviation is kept while the dispersion is eliminated, so that, in the telescope, we have a nearly white image of anything which

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this direct-vision arrangement is getting into common use. I have here another direct-vision arrangement which is well worthy of being brought to your notice. It does not depend at all upon the principles I have just been trying to explain to you. It is called the Herschel-Browning direct-vision spectroscope, in which the ray is refracted and reflected internally, in the prisms themselves. We have therefore, in addition to the simple prism which I formerly brought to your attention, two other aids to research of extreme value in certain classes of observations. The direct-vision spectroscopes which are now sold are made on one of the two principles just described; some of them are made so small that they can be easily carried in the waistcoat-pocket, and still are so powerful that all the principal, and many of the less prominent, lines in the solar spectrum may be seen with them.

gives us ordinary light, although, as you know, it is by
the deviation alone that we are enabled to get the magni-
fied image of that object. So also in the spectroscope we
have an opportunity of varying the deviation and the dis-
persion. By a converse arrangement we can keep the
dispersion while we lose the deviation; in other words,
we have what is called a direct-vision spectroscope. If
we take one composed of two prisms of one kind of
glass which possesses a considerable refractive power,
and three prisms of another kind which does not re-
fract so strongly, arranged with their bases the opposite
way, the deviation caused by the two prisms in the
one direction will be neutralised by the deviation of
the three prisms in the opposite direction; whilst the
dispersion by the three prisms, exceeds that which is
caused by the two prisms in the opposite direction, the
latter dispersion therefore will neutralise a portion only
of the dispersion due to the three prisms. The final
result is that there is an outstanding dispersion after the
deviation has been neutralised, so that when we want
to examine the spectrum of an object we no longer have
to look at it at an angle. No doubt you recollect the
angle that was made by the light the moment it left the
prism, but we have an opportunity, by this arrangement,
of seeing the spectrum of an object by looking straight
at the source of light in the application of spectrum
analysis, especially to the microscope and telescope,
this modification-due to M. Janssen, the well-known
astronomer, who was the first to bring it into general
notice is one of great practical importance, so that in transparent.
any research which does not require excessive dispersion,

Of the special application of the spectroscope to the microscope I need say but little now. The spectroscope thus used is a direct-vision one, this form being far more convenient for attaching to the microscope. The light which illuminated the object in the microscope was first of all passed throu h a prism; but in later arrangements it passes through the prism in its passage from the object. This is obviously a much better plan, because, in the first instance, you could only deal with transparent objects; but here, as you deal in any case with the light that comes from the object itself, it is quite immaterial whether the object be opaque or J. NORMAN LOCKYER (To be continued.)

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