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they were pushed on from behind? And now, if you can spare me a few minutes more, I will show you from the Blue-books what effect their apparent acquiescence in Kaufmann's breach of the Czar's engagement had upon the mind of the Ameer.

A. Go on, go on. You are having it all your own way.

B. Pull me up whenever you please, if you find me departing from the authorised record of facts. The Ameer knew of our engagement with Russia. The Indian Government had informed him of it. Presently Kaufmann also wrote him a friendly letter, alluding to the existence of the engagement as a subject for congratulation. The Ameer was perplexed at this (p. 65). Russia and England in cordial agreement about his territories! This is a new tone. God knows what State secrets may be concealed in it!' He gave the letter to our Cabul Agent to be transmitted to the Viceroy. More letters came from Kaufmann. The Ameer gave them also to the Agent, more perplexed than ever. The Indian Government said nothing to him about these messages. They did not at once declare that they were a breach of Russia's engagements, and inform him that they would not permit it. What conclusion could he come to? He found Russia breaking her engagements: he furnished the English Government with the proofs. They made no remonstrance that he was aware of, and little that anybody is aware of. What conclusion could he come to, except that Russia was the stronger Power, and that the English Government was afraid to hold her to her pledges?

A. But stay. At p. 177, in a letter from the Commissioner of Peshawur to the Ameer, replying to his plea that if he accepted an English Mission he could not decline a Russian one, because Russia was a great and fearless Power,' I find this

The Ameer must be aware that the British Government, acting on behalf of His Highness's wishes and interests, has obtained from the Government of the Czar written pledges not to interfere, directly or indirectly, in the affairs of Afghanistan.

The reception of a British Envoy cannot therefore necessitate the reception of a Russian one; for in refusing to receive a Russian Envoy, His Highness would only be acting in conformity with the policy thus solemnly agreed upon.

B. That refers to the reception of a Russian Envoy, but at the time when it was written (8th of July, 1876) the Indian Government was permitting, without remark, the Ameer's reception of Kaufmann's informal messages. If they permitted this, how was he to know that they had the will or the power to protect him if he should decline to receive a Russian Envoy? I say that the Ameer, hedged in as he was, could draw only one of two conclusions: either that the English were afraid of the Russians; or that they had made a compact to manage his affairs between them, and that the Russian annexation of Kokand, of which Kaufmann had informed him, was the prelude to an English annexation of Afghanistan.

A. Now you are going a little too deep into the feelings of the savage for me. After all, the main point is that, however it came about, he accepted a Russian Envoy and refused an English Envoy, and that this is a thing which we could not permit.

B. Not even if we had forced him into the arms of Russia by our blundering diplomacy?

A. Certainly not.

B. Not even if there was another clear course open to us? I grant you that we could not permit a Russian Envoy to remain at Cabul. A. Well, that might alter the case. But what other course was there? You can't tell me that from the Blue-books.

B. There is no record in the Blue-books of any compact with us broken by the Ameer in receiving a Russian Envoy. On the other hand, the passages I have shown you, and the one you have just quoted yourself, make it clear that there was a compact with Russia that she would not send Envoys to Cabul. Why not call Russia to account? The Ameer had broken no compact, Russia had; why hector the small man about the offence of the big?

A. I must be going now.

B. I hope I have convinced you, without the least reference to party, which should never be allowed to interfere with the foreign policy of this country, that a course of action, decided on after due consideration of all contingencies, to prevent unrest and uncertainty, has been broken in upon without a shadow of a reason. Further, that the safeguards to our interests in India, provided by an experienced statesman after repeated and careful consultatiou with all his high officers who were practically conversant with the state of affairs, have been ignominiously and pusillanimously neglected by an inexperienced statesman, intent upon his own doctrinaire ideas, the fruits of a few months' cram. You see for yourself in these Blue-books with what amount of propriety the men who have gratuitously disturbed the tenure of our power in India try now to prove that they could not help it, and to throw the responsibility and the blame on other shoulders. No one who looks at these colourless records can be in any difficulty about putting the saddle on the right horse.

A. Well, well; I must be going.

B. I hope you are convinced.

A. Not in the least.

B. Do you reject the evidence of facts?

A. throws Blue-books in the fire; B. rescues them, and
remarks that A. is an awful example of the saying-
'Give a falsehood an hour's start, and it will run
round the world. A. retorts by speaking of facts in
disparaging language; and a temporary breach is
made in a lifelong friendship.]

WILLIAM MINTO.

RECENT SCIENCE.

(PROFESSOR HUXLEY has kindly read, and aided the Compilers and the Editor with his advice upon, the following article.)

To those who have been familiar for many years with the electric light, and have watched its gradual application to special purposes of illumination, it is strange to find it suddenly starting into publicity and overshadowing all other scientific topics. The impetus which has lately been given to the subject of electric lighting may undoubtedly be traced to the invention of the famous 'electric candle' of M. Jablochkoff, and to the introduction of this candle on an extended scale into some of the great thoroughfares of Paris. Those who had admired the beautiful effect of the Jablochkoff light in the Avenue de l'Opéra, would naturally believe that we were approaching the dawn of a new era in the history of illumination. No sooner, however, does the light give promise of practical utility, than a host of inventors rush into the field, each enthusiastic on the peculiar merits of his own system, until the unscientific reader is utterly bewildered by the number and variety of devices which clamour for attention. The excitement on this question has culminated in the mysterious paragraphs which, after their appearance in the American newspapers, have been widely reproduced in this country, announcing that Mr. Edison, who has lately played so prominent a part in connection with other electrical discoveries, has devised a new system of electric illumination which is so simple and so practical as to threaten to supersede the use of coal-gas. The details of his process, it is true, have not yet been published; but still sufficient has leaked out to leave little room for doubt that the light is obtained by the incandescence of a resisting body interposed in a closed circuit. It may therefore be of interest to explain the principles on which such incandescence is produced; to trace the steps which have previously been taken to apply this incandescence to practical purposes; and to contrast this mode of illumination with that of the ordinary electric light.

When an electric current such as that from a voltaic battery meets with a resistance to its passage, the electricity is directly converted into heat. It is, in fact, a case of the transformation of one species of energy into another. If a thin wire be placed in the circuit, the

temperature of the wire rapidly rises; and it has long been known that the amount of heat thus generated is directly proportional to the electric resistance of the wire. Now the resistance depends, among other things, on the nature of the metal; those metals which are good conductors, such as silver, offering much less resistance than those which are bad conductors, such as platinum. It was shown many years ago by Mr. Children that if a chain be built up of links alternately of silver and of platinum, and if a current of suitable intensity be sent through this chain, the platinum links may glow vividly, while the neighbouring links of silver remain dark and comparatively cool. From its low electric conductivity—or what comes to the same thing, from its high resistance-platinum is peculiarly fitted for exhibiting incandescence.

It should be remarked that the resistance which a platinum or other wire offers to the current is related not only to the nature of the metal, but also to the thickness of the wire. Reduce the thickness, and the resistance is immediately increased. Again, the heating effect is closely connected with the strength of the current. Hence a powerful current sent through a thin platinum wire immediately renders it incandescent. Many attempts have been made to utilise the brilliant light which is thus emitted. As far back as 1845 a patent was granted to Mr. E. A. King, of London, for a method of obtaining electric illumination by the incandescence of either platinum or carbon. In one form of his lamp a narrow strip of platinum-leaf is held vertically between suitable conductors, and rendered luminous by a properly-regulated current; the whole arrangement being protected by a glass globe which screens the incandescent metal from currents of air. Other patentees have advocated the use of iridium—a metal of extreme rarity which is closely related to platinum, both in its physical characters and in its mode of occurrence in nature. Thus Mr. Petrie, in 1849, obtained a good light by the incandescence of iridium, or of one of its alloys; and the latest news from America states that the metal which Mr. Edison employs is an alloy of platinum and iridium.

If the current which is struggling to force a passage through a fine wire, or through a thin strip of metal, be sufficiently powerful, the heat rises to such an intensity that the metal becomes fused. Even a substance so refractory as platinum may thus be readily melted. The fusion, of course, breaks the continuity of the circuit, and the current is consequently interrupted. To avoid this and other sources of annoyance Mr. King proposed, in his patent cited above, to employ thin rods of carbon-a material which may be exposed to intense heat without either fusion or volatilisation. When the carbon is heated to whiteness in air it is rapidly oxidised, and to avoid this consumption of the rod, it was suggested to enclose it in a 1 Specification of Edward Augustin King, November 4th, 1845, No. 10919.

glass globe, attached to a long tube, from which all air had been expelled by first filling it with mercury, and which formed in fact the expanded upper portion of a barometer.

Nothing had been heard for many years of King's lamp, and most subsequent methods of electric lighting had been based on entirely different principles, until in 1873 attention was again called to the production of light by the incandescence of carbon.2 The subject was revived by M. Lodyguine, a Russian physicist, who submitted to the Academy of Sciences of St. Petersburg a lamp which was considered to be so novel in construction, and so promising as a practical source of light, that the Academy, apparently ignorant of what had been done in the same direction in this country, awarded to him the Lomonossow prize. In Lodyguine's lamp the rod of carbon through which the current passes is cut thin in one portion of its length, and as the electric resistance is therefore greater here than elsewhere, it is this portion alone that becomes incandescent.

A lamp precisely similar in principle to Lodyguine's, but more ingenious in its construction, was patented in 1875 by M. Konn, of St. Petersburg. It should be remarked that even in an exhausted vessel the incandescent carbon is gradually destroyed. In Konn's lamp, therefore, several carbon rods are placed side by side, and as soon as one rod is destroyed another is automatically brought into the circuit. In this way the light may be maintained uninterruptedly for several hours, and the lamp has indeed been practically used in the illumination of a large warehouse in St. Petersburg.

Another Russian inventor, M. Bouliguine, has devised a similar lamp, in which the light is kept up with only a single rod of carbon. This rod is of great length, and slides up and down in a tubular holder, which is so constructed that as soon as the incandescent portion is destroyed, the rod moves up and brings a fresh portion into its place. That part of the rod which emits light is securely held between conical jaws of carbon, which allow free passage to the electricity, and it is therefore only the exposed portion of the thin rod which offers sufficient resistance to become a luminous focus.

The various methods of obtaining light by the incandescence of a resisting medium-whether that medium be a metal of low conductivity, or a thin rod of carbon-are entirely different from those which are employed in producing that brilliant source of illumination which is specially distinguished as the electric light. This light was first obtained by Sir Humphry Davy, in 1813, by means of the

* See Electric Lighting: a Practical Treatise, by Hippolyte Fontaine. Translated from the French by Paget Higgs, LL.D. (Spons, 1878). So much has been lately written on the subject of this article, that it is needless to give references to the various technical journals, but the two following pamphlets may be referred to:On the present state of Electric Lighting, by J. N. Shoolbred, B.A. (Hardwicke and Bogue). And Electric-Lighting: its state and progress, and its probable influence upon the Gas interests, by John T. Sprague (Spons).

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