June 25. 1908] 



NA TURE 



183 



that, even could the mechanical difficulties of construction 

 be overcome, refractors of greater dimensions than the 

 40-inch cannot be constructed with the hope of uniform 

 performance at all altitudes. 



The same journal contains a discussion by Prof. Hart- 

 mann of an improvement of the Foucault knife-edge test 

 in the investigation of telescope objectives. 



The Temperature of the Sun. — In a preliminary note, 

 now published as an abstract from the Anna\cn dcr Physik 

 (vol. .\xv., pp. 905-20, igo8), Dr. Goldhammer discusses 

 anew several sets of results obtained in the determination 

 of the temperature of the sun. From the discussion of 

 Langley's various observational data he arrives at the con- 

 clusion that the probable actual temperature of the sun is 

 not less than 10,000° absolute. 



The Varwtion of the Pole. — Prof. Albrecht's annual 

 summary, for 1907, of the provisional results derived from 

 the observations made at the various international latitude 

 stations appears in No. 4253 of the Astronoitiisclic Nach- 

 richten (p. 73, June 5). The extrapolated values for the 

 variation, in the several coordinates, for 19080 are : — 

 x=— o"-097, y=-l-o".i85, and s=+o"-oi2. The curve 

 showing the departure of the pole from the mean position 

 between i8qq-q and 19080 shows that the value of the y 

 variation at the commencement of the current year was 

 approaching the maximum observed during that period. 



Observations of the Perseid Shower in 1907. — No. 

 42^3 of the Asironomische Nachrichten (p. 83, June s) 

 contains a note by Prof. J. Sykora in which are given 

 the results of the meteor observations made at Tashkent 

 and Iskander during the nights of August 10-12, 1907 ; 

 Iskander lies about 44 kilometres to the north-east of 

 Tashkent. From the recorded paths of 178 Perseids the 

 centre of the radiant of the shower, for 1907, was found 

 to be o = 42°7, 5=-(-53''-8, and the area covered by the 

 radiants lay between 31° and 55° in R.A. and -|-49° and 

 -1-59° in declination. The calculation of the altitudes 

 showed that the mean heights of appearance and disappear- 

 ance were 167 and 96 kilometres respectively. The trails 

 of nine meteors were photographed, and brief descriptions 

 of trails are given in the paper ; several of them indicate 

 marked variations of brightness during the meteor's flight. 



RECENT DEVELOPMENTS IN ELECTRIC 

 LAMPS. 



T N an article which appeared in Nature last June the 

 -'■ present writer reviewed briefly some of the improve- 

 ments which had been made and promised in incandescent 

 electric lamps. .^t tlie time that article was written, 

 matters were in a condition of considerable uncertainty 

 on account of the great number of new developments whicli 

 had been announced, the value of which was, to a very 

 large extent, uncertain. The frequent announcements of 

 these improvements, which were appearing almost weekly, 

 led electrical engineers to feel considerable hesitation In 

 adopting any new lamp for fear that it should be super- 

 seded almost immediately after its adoption. Since that 

 time the position has become much quieter, and during 

 the past si.x months the solid progress which has been 

 made in the introduction of these lamps on the market 

 has been remarkable. Now that considerable experience 

 has been obtained of the practical working value of the 

 different types of lamp, a favourable opportunity is afforded 

 of taking a general survey of the present position and 

 prospects for the future. At the same time, a similar 

 survey may be taken of the conditions existing in the field 

 of arc lighting, in which the developments during the past 

 two or three years have been almost equally noteworthy. 



Incandescent Lamps. 

 As was pointed out in the article referred to above, the 

 only two lamps which appeared to merit particular atten- 

 tion were the tungsten and the tantalum lamp. The 

 tantalum lamp has now been in practical use for about 

 two years, and has not undergone any appreciable modifi- 



NO. 2017, VOL. 78] 



cation since the time of its first introduction. Difficulties 

 of producing a satisfactory lamp for use with alternating 

 current are still not overcome, and the difficulties of draw- 

 ing tantalum wire sufliciently fine to enable either low 

 candle-power low-voltage, or medium candle-power high- 

 voltage lamps to be produced still await practical solution. 

 It is true that the range of candle-power witli low-voltage 

 lamps has been extended by the introduction of a 16- 

 candle-power lamp, and that announcements have been 

 made from time to time that a satisfactory solution has 

 been found for the manufacture of high-voltage lamps. 

 The fact remains, however, that high-voltage lamps are 

 not yet produced commercially. The tantalum lamp has 

 satisfactorily proved its value for electric lighting. 

 Although the general results obtained seem to show a 

 comparatively short average life of about 700 hours, and 

 though the efficiency is approximately only half that of 

 the newer tungsten lamp, it is apparent that this lamp 

 will have to be reckoned with for some time to come as 

 a very important factor in the field of incandescent electric 

 lighting. Though it may not be able to compete on the 

 score of efficiency with the tungsten filament, yet the 

 greater strength of the filament must always operate to 

 counterbalance these disadvantages. 



The tungsten lamp, ever since its commercial introduc- 

 tion into this country under the name of the " Osram " 

 lamp by the General Electric Company, has made rapid 

 strides in popularity. Considering that the lamp has only 

 been on the market for a matter of about nine months, its 

 very widespread use at the present time must mark almost 

 a record in the development of electric lighting. In its 

 practical performance, also, this lamp has fulfilled, or 

 more than fulfilled, the hopes which were raised for it 

 before its introduction. Beyond the blackening which 

 occurs with a small percentage of these lamps, the general 

 experience is that a life of 1000 to 1500 liours is obtained 

 almost without any decrease in the initial efficiency of about 

 ij watts per candle. This blackening appears to be a 

 defect in manufacture wlnich will doubtless be soon over- 

 come, since it is not a characteristic of all lamps, but is only 

 observed in a very small percentage, which generally show 

 this defect almost immediately they are put into use. 

 The tungsten lamp has hitherto possessed the disadvantage, 

 when compared with its tantalum rival, that it could only 

 be used in a vertical position, but a modified type has 

 just been introduced which can be burnt at any angle. 

 On the other hand, the tungsten lamp has the advantage 

 that it is suitable for use on either direct- or alternating- 

 current circuits. Up to the present, the range of voltage 

 for which the lamps can be made is practically the same 

 as that for the tantalum lamps, viz. voltages up to 130, 

 but the tungsten lamp has not yet been made for voltages 

 of 100 in such low light units as the tantalum lamps, the 

 lowest at present obtainable being approximately thirty 

 candles. Tungsten lamps have also been made, but not 

 vet commercially introduced, for high voltages (200 and 

 above), and the introduction of a 40-candle-power lamp 

 for 200 volts is promised very shortly. 



It is yet too early to say precisely what will be the 

 effect of the introduction of these two lamps on electric 

 lighting in general. At present, for the most part prob- 

 ablv, the lamps have been used for the lighting of factories, 

 shop windows, and public or semi-public places where 

 costs of lighting are very closely considered and artistic 

 effects are of secondary importance. It is perhaps not 

 safe to argue from the success which the lamps have 

 attained in the past year for these purposes that they will 

 meet with corresponding success in private house light- 

 ing, especially as in that case the size of the light unit 

 becomes of much greater importance. It is more than 

 probable, however, that the general public will welcome 

 the higher light units if they provide them, as these lamps 

 do, with a means at the same time of actually reducing 

 their lighting bills. The present writer, for example,^ has 

 substituted two 32-candle-power Osram lamps for a single 

 i6-candle-power carbon filament lamp, and finds that it 

 has resulted in actual saving in money in spite of the fact 

 that four times as much light is obtained. It is note- 

 worthy that the fears which were expressed that the 

 difficulties in running lamps in series would very seriously 



