February 3, 19 16] 



NATURE 



633 



much larger than they were a few years ago, and the 

 rays they produce will penetrate several centimetres 

 of steel, and allow a radiograph of the thickest part 

 of the body to be taken by means of a tube three 

 metres away. At the commencement of the war the 

 military authorities requisitioned all the X-ray tubes 

 in France, but as this supply was found insufficient 

 for the proper equipment of the radiological stations, 

 the two French manufactories, which had been closed 

 owing to their directors being called to the colours, 

 were reopened, in one case by the recall of the director 

 from the front, in the other by the appoinment of a 

 member of the Academy of Sciences as director. Under 

 the guidance of a professor of the College de France 

 a firm of glass-makers began the manufacture of the 

 special glass for the bulbs, and in a few days was 

 turning out the necessary quantity, so that France is 

 now producing sufficient X-ray tubes to meet her own 

 requirements, and is supplying some to her Allies. 



The essentials in the manufacture of a good rheo- 

 stat are the use of first-class material and workman- 

 ship of a high grade. This useful piece of apparatus 

 should therefore be particularly a British product ; 

 the rheostat cannot be considered to be a "competi- 

 tive " article or one lending itself particularly either 

 to what the Germans term " Massenfabrikation " or 

 to dumping. Yet Messrs. Isenthal and Co., in send- 

 ing us a new list of their rheostats, frankly admit 

 that they had previously imported these from abroad, 

 but are now manufacturing them entirely in England. 

 The list before us is one of the most complete we 

 have seen. Both the flat slate and the tubular types 

 have hand-shield sliders with well-designed contact- 

 makers, and the number of different arrangements 

 listed should meet practically every requirement. A 

 useful variation from the ordinary flat type is one 

 with limbs of cross-shaped section which affords 

 increased ventilation and enables the maximum num- 

 ber of watts to be dissipated for the minimum dimen- 

 sions without undue heating. In the tubular type 

 the slate bars are replaced by fire-enamelled steel 

 tubes, and the resistance wire is oxidised so that 

 the insulation of the oxide enables the turns to be 

 wound closely. Dimensions, approximate resistances, 

 weights, and diagrams of connections and arrange- 

 ments of the terminals are given in detail, so that 

 it should be possible to order rheostats for almost 

 any purpose directly from the catalogue. We trust 

 that Messrs. Isenthal and Co. will continue to manu- 

 facture them in England after the war. 



There is a description of one of the new British 

 projectile-making factories given in Engineering for 

 January 28, illustrated by several good photographs 

 showing some of the shops. The nine bays of the 

 factory cover about 196,600 sq. ft., and are arranged 

 so as to reduce to the minimum the distance which 

 the shell has to travel in the process of manufacture. 

 From the entry of the rough bar to the finished shell 

 ready to be put into the breech of a gun, the distance 

 travelled is only 400 yards. There are nearly one 

 hundred operations in making a shell, and many of 

 these take but little time ; hence it is important that 

 the time spent in moving the shell from operator to 

 NO. 2414, VOL. 96] 



operator should be as small as possible. Small shells; 

 are machined in this factory by female workers, and 

 there are 1800 women in this department. The girls 

 are able to work the machines in three days, and are 

 efficient in seven days ; the highest efficiency is attained 

 after two months' experience. One skilled worker 

 suffices for the setting of the machines for twelve female 

 operators. The accuracy demanded is 0004 in., and 

 it speaks well for the girls that the rejected shells da 

 not amount to more than one per cent. 



OUR ASTRONOMICAL COLUMN. 



The Solar Eclipse of February 3, 19 16.— Official 

 European observatories have perforce had to refrain 

 from participating in the observation of to-day's total 

 solar eclipse, notwithstanding the fact that spectro- 

 scopic interest was so unexpectedly intensified by the 

 change recorded in the coronal spectrum at the eclipse 

 of August 21, 1914. From the success that then 

 attended the Spanish expedition, it might almost have 

 been expected that the Madrid observers, at any rate, 

 would have attempted to take advantage of the present 

 opportunities. It would appear, however, that the 

 American observers will have the field to themselves. 



Starting in the Pacific Ocean, February 3^. ah. 29m. 

 G.M.T., in long. 121° 356' W., lat. 7° 208' N., almost 

 a minimum part of the central line of totality passes, 

 over land areas. This portion is nearly parallel to and 

 somewhat north of the Bogota-Caracas line in Columbia 

 and Venezuela. The line then crosses the Caribbean 

 Sea to Guadeloupe. The duration of totality over all 

 this section is about 2^ minutes ; the maximum of 

 2m. 36s. is reached before quitting Venezuela. Sweep- 

 ing across the Atlantic, centrality passes a little 

 wide of the Azores, and ends about 200 miles off the- 

 south coast of Ireland (Mizen Head) at 5h. 310m., in. 

 long. 9° 502' W. and lat. 49° 23-8' N. A partial 

 eclipse will consequently be visible over the greater 

 part of the Americas. 



In south-west Europe, north-west Africa, and the- 

 British Islands the eclipse will only be partly visible,, 

 the sun setting in partial eclipse. At Greenwich the 

 eclipse begins at 4h. 31m., and the sun sets at 4h. 49m.,. 

 with about one-quarter of the disc obscured. The 

 magnitude of the eclipse increases as the observer is 

 situated further west, until in the south-west of Ireland: 

 the obscuration reaches about nine-tenths of the disc. 



Comet 19156 (Taylor). — Prof. E. Stromgren has. 

 sent to Nature his latest observation of the position 

 of this comet, made on January 23. At 5h. 47m. 6s.. 

 G.M.T. the comet's position was a app., 5h. lom. 

 1-895., 8 app. +16° 56' 54-1", whence the corrections; 

 of the ephemeris of Copenhagen Circular No. 11,. 

 Aa = os., A8=+o-8' The comet is stated to have been: 

 of the eleventh magnitude. 



Colours of Stars in the Clusters N.G.C. 1647 

 AND M. 67. — The first statistical investigation employ- 

 ing the colour classes recently proposed by Prof. F. H. 

 Scares deals with the distribution of colours among 

 the stars in the above clusters (Proc. Nat. Acad, of Sci.> 

 i., p. 483). Hertzsprung and Seares have respectively 

 published effective wave-lengths and colour indices for 

 a number of the stars in N.G.C. 1647 (Nature, Sep- 

 tember 23, 1915). Hertzsprung's results were alone- 

 taken into account, leading to the following corre- 

 spondences between effective wave-length and colour 

 class : — 



Effective w.l. 4190 4260 4330 4400 4470 4540- 

 Colour class bo ao fo go ko mo. 



N.G.C. 1647 is principally made up of a and / stars,, 

 but contains a number of b and also some km, whilsf 



