June 25, 1908] 



NA TURE 



185 



illuminants. Attempts have been made to improve the 

 colour by introducing other metals, such as metals of the 

 alkali group, into the tube, but these have not hitherto 

 proved successful. It is stated, however, that a very 

 marked improvement has been effected by the firm of 

 Heraeus, in Germany, by adopting quartz tubes instead 

 of glass tubes, and pushing the temperature at which the 

 arc is run up to very much higher limits. By working 

 the lamp at such a current density that the internal 

 pressure in the tube is approximately one atmosphere, it 

 is stated that the efficiency of the lamp is more than 

 doubled, and that a continuous spectrum is added to the 

 line spectrum of the mercury, thus giving the light a quite 

 pleasant and almost normal colour. These quartz-tube 

 lamps have the additional advantage that under the con- 

 ditions of working the length of tube for a given voltage 

 is very much less than when glass tubes are used. The 

 commercial introduction of these lamps is promised for 

 this year. 



Reference might also be made to one other type of 

 electric lamp which has during the past year come into 

 commercial use, namely, the Moore tube lamp. This lamp 

 is simply an ordinary vacuum tube of great length, and 

 operated at a very high voltage. Tlie tubes, which are 

 if inches diameter, can be made up to 200 feet in length, 

 and are fixed up in position by welding together short 

 lengths of tube, high-voltage supply being obtained by 

 means of a transformer the secondary terminals of which 

 are connected to graphite electrodes in the tube. The 

 essential feature of this lamp is the method which has been 

 adopted to overcome the difficulty that the vacuum de- 

 creases as the lamp burns, owing to the absorption of gas 

 by the glass tube. In order to maintain the vacuum 

 constant a most ingenious valve is employed. The main 

 tube communicates by means of a branch with the outer 

 air, this branch tube being sealed by a porous carbon plug 

 covered with mercury. The level of the mercury can be 

 altered by the rising or falling of a float ; in one position 

 of the float the carbon plug is completely covered, in the 

 other it is partly uncovered. The movements of the float 

 are controlled by a solenoid connected in series with the 

 primary of the transformer supplying the tube. When the 

 vacuum falls the conductivity of the tube increases and the 

 primary transformer current rises ; this lifts the mercury 

 float and causes the mercury level to fall, uncovering 

 the point of the carbon plug and allowing a little air to 

 fiher into the tube. The conductivity of the tube is thereby 

 decreased, the primarv current falls again, and the porous 

 plug is again completely covered with mercury. It is 

 stated that this valve, which operates normally about once 

 a minute, maintains the vacuum in the tube, which is in 

 the neighbourhood of o-i mm. of mercury, constant 

 within 10 per cent. 



The only installation of this lamp In this country is 

 tliat in the courtvard of the Savoy Hotel, and those who 

 have seen this will probably agree that the light represents 

 in manv respects the ideal form of artificial lighting. Tlie 

 colour of the light given by the tube depends upon the gas 

 which it contains, and is pure white for carbon dioxide, 

 slightlv pink for nitrogen or air. Nitrogen is stated to 

 be twice as efficient as carbon dioxide, and slightly more 

 efficient than air. When it is desired to operate the tube 

 with either of these gases the open end of the valve is 

 connected to either a phosphorus tube (to extract the 

 oxygen from the air drawn in) or to a gas apparatus 

 generating carbon dioxide by the action of acid on marble. 

 The efficiency of these lamps is difficult to determine, but 

 appears to be in the neighbourhood of i-6 to i-8 watts 

 per candle. 



It is interesting to note that the improvements described 

 above in incandescent and arc lamps have once again 

 brought electric lighting on practically the same level for 

 cheapness as gas lighting. The introduction of the gas 

 mantle gave gas lighting so great a superiority on the 

 score of cheapness that for a great many years it has only 

 been possible for electricity to hold its own on account 

 of its many other advantages. Just as the ordinary gas 

 mantle beat the carbon filament lamp, the high-pressure 

 gas-mantle systems competed on an equal, or even on a 

 slightly better, basis with arc lighting. The whole com- 

 plexion which appears is now changed, since the i to 15 



NO. 20I7. VOL. ^81 



watt metal filament lamps can compete with the ordinary 

 mantle for small lighting, and flame lamps are 

 superior to the high-pressure gas lamps. It must bo 

 remembered that, from a scientific point of view, the 

 efficiency of electric lamps is vastly superior to any type 

 of gas lamp, the main cheapness of gas lighting being 

 entirely due to the difference between the cost of power 

 delivered to the lamp in the form of gas and in the form 

 of electric energy. It is interesting to remark that whereas 

 the improvements in gas lighting have been effected by 

 departing from an incandescent flame to an incandescent 

 solid, the improvements in arc lighting have been obtained 

 by a move in exactly the opposite direction. 



In conclusion, attention may be directed to the honour- 

 able position occupied by this country in the developments 

 of electric lamps. A little more than a century ago an 

 English philosopher, Sir Humpliry Davy, discovered the 

 electric arc. Thirty years ago an English inventor. Sir 

 Joseph Swan, shared with an American, Edison, the dis- 

 tinction of overcoming the difficulties attendant upon the 

 production of an incandescent electric lamp of small candle- 

 power. With these two names England's connection with 

 the development of electric lighting begins and ends. The 

 first satisfactory arc-lamp carbons were made by Carr6 

 (France). The invention of the cored carbon is due to 

 Siemens (Germany), the practical realisation of flame 

 carbons to Bremer (Germany), and their further develop- 

 ment to the Continental manufacturers and to Blondel 

 (France). The magnetite arc has been developed by Stein- 

 metz and the General Electric Company of America. The 

 mercury arc was shown to be practical by Arons 

 (Germany), and was perfected by Cooper-Hewitt (America). 

 Its latest development is due to the firm of Heraeus 

 (Germany). The vacuum-tube lamp we owe to McFarlane- 

 Moore (America). In incandescent lighting the only radical 

 improvement which has been effected in the carbon fila- 

 ment is the metallised filament of the General Electric 

 Company of America. The Nernst lamp is due to Prof. 

 Nernst and the A. E.G. of Germany. The first metal 

 filament lamp was the " Osmin " lamp of Welsbach 

 (Germany), which was followed by the tantalum lamps 

 of Siemens (Germany) and the tungsten lamps which were 

 perfected by Welsbach (Germany), Just and Hannaman 

 (.Austria), and Kuzel (Austria). 



One may well ask what is the reason for this un- 

 satisfactory state of afi'airs. The actual reason is not far 

 to seek. In the field of scientific discovery England has 

 alwavs been, and still is, in the front rank, but not any of 

 the improvements enumerated above are in the nature of 

 discoveries, but are all inventions of a type which have 

 been, and can only be, developed by years of costly ex- 

 periments carried out always with a commercial end in 

 view, a form of research which is for the most part carried 

 out in the laboratories which are to be found attached to 

 the more important Continental and .\merican factories. 

 The question therefore reduces to asking why it is that 

 these laboratories are not to be found in connection with 

 English works. If you ask the manufacturer, he will prob- 

 alilv answer that with unprotected markets, unrestricted 

 competition, and the uncertainty of being allowed to enjoy 

 the fruits of his labour, he cannot afford to spend a share 

 of his money in the prosecution of costly research which 

 may onlv after many years, and possibly never, yield 

 results. If you ask the man of science, he will probably 

 tell you that it is due to the complicated set of facts which 

 were summed up bv Prof. Perry in the words " England's 

 neglect of science,''' of which the most striking examples 

 are afforded by the position which science takes in all our 

 systems of education, and by the attitude of indifference, 

 amounting almost to contempt, which is directed towards 

 it bv all our Governments, our men of means, our manu- 

 facturers, and almost all classes of the community. Each 

 answer probablv comprises part of the truth, and the two 

 together possibly comprise the whole, and whilst everyone 

 is agreed that something ought to be done, we are all 

 too busy arguing which is the best specific to take any 

 steps towards a remedy. In the meantime, further 

 developments are being 'worked out abroad, and every 

 year is making it harder for this country to make up the 

 leeway which it has lost and is losing. 



Maurice Solomon. 



