580 



NATURE 



[December 29, 1921 



cesses," for no one can properly appreciate any sub- 

 ject unless he is acquainted with at least the outlines 

 of its history. The tables given in this almanac are 

 so numerous that some of the older ones have occa- 

 sionally to be omitted to make room for others, but 

 the omission is largely compensated for by a list of 

 those not included, with the most recent year of the 

 almanac in which each may be found. 



A CHEMICAL examination of a Babylonian glass vase 

 of a date approximately looo B.C. is described in the 

 Chemiker Zei^tung of November 15 by Dr. F. Rathgen. 

 It appears to have been formed by the application of 

 soft glass to the outside of a clay shape, and has 

 been but little attacked by the soil-water. The glass 

 was white and opaque, the presence of microscopic 

 white fused spherules being observed. Analysis gave 

 silica, 7332; alumina, and ferric oxide, 11 78; calcium 

 oxide, 586 ; potassium and sodium oxides, 446 ; and 

 cupric oxide, 3 88. The vase was decorated by oval 

 to circular lenticular pieces of glass fused on the 

 body. A piece of magnesite from the same period 

 showed borings which indicate the use of a tubular 

 boring instrument with the addition of an abrasive, 

 possibly quartz. Such instruments, belonging to the 

 Neolithic period, have previously been described. A 

 finger-ring of metallic tin is also referred to. A 

 method of detecting indigo in coloured fabrics, depend- 

 ing on its sublimation in a current of carbon dioxide 

 at 230° C, showed its presence in the garment of an 



Egyptian princess of the year 1000 B.C.. Indigofera 

 argentea occurs in Egypt. 



Generally speaking it is found more economical to 

 utilise the whole of the available head in a reservoir 

 system intended for domestic water supply to over- 

 come the frictional resistance in the supply mains, 

 rather than to attempt to use it also as a source of 

 power. Occasionally, however, where multiple re- 

 servoirs are used, and where these are at different 

 elevations, or where a constant flow of compensation 

 water is available, it is possible to develop an appre- 

 ciable amount of power at the expense of a head which 

 would otherwise be wasted. An interesting example 

 of this is to be found in connection with the water- 

 works of the Bradford Corporation in the higher 

 reaches of the Nidd. Here advantage has been taken 

 of an existing high-level reservoir at the head of 

 the Nidd Valley. The new reservoir is now under 

 construction at a lower level, and the discharge from 

 the higher reservoir is being utilised to drive a hydro- 

 electric plant, which will supply the power required 

 for operating the ropeways, cranes, crushers, and 

 other machines required for the building of the dam, 

 and for lighting the improx-lsed village where the 

 workers will live. The power-house contains two 

 300 h.p. turbines, each directly coupled to a three- 

 phase alternator of 200 kw. capacit}- at 2200 to 2400 

 volts. Messrs. Vickers, Ltd., have been responsible 

 for the construction of the hvdro-electric scheme. 



Our Astronomical Column. 



The January Meteors. — Mr. W. F. Denning 

 writes: — "The opening nights of every New Year 

 are marked by an abundance of meteors, though they 

 vary in number at different returns, and are some- 

 times altogether obscured by clouds. The best time 

 to look for them at their next appearance will be in 

 the two hours preceding 7 a.m. on January 4, but 

 they may also be plentiful on the morning and evening 

 of January 3. This particular shower furnishes con- 

 spicuous objects with long flights of moderate speed. 

 The radiant point is usually in 230°+ 54°, and this is 

 near the northern horizon at about 8.30 p.m. An 

 hour before sunrise, however, the position is high in 

 the north-east and situated far more favourably for the 

 distribution of meteors. 



"This particular system has not been hitherto asso- 

 ciated with any known comet, but it is highly probable 

 that it is connected with some body of this kind which 

 ■existed in past times, and possibly exists to-day." 



The shower appears to have become definitely visible 

 at an earlier period than usual at this return. 



On December 20 a bright meteor was seen by Miss 

 ■Cook at Stowmarket and by Mr. F. Sargent at the 

 University Observatory, Durham. A comparison of 

 the recorded paths indicates the radiant point at 

 229° + 6o° and the height of the object from 72 to 

 55 miles over the region of Surrey. 



On December 23 several meteors, including a bril- 

 liant one at 8 p.m., were observed from Bristol from 

 the same shower, and there seems no doubt that the 

 display of Quadrantids is prolonged over a rather 

 considerable period, though it furnishes a really 

 abundant display over a few hours only. 



NO. 2722, VOL. 108] 



The Furthest Cluster. — The cluster N.G.C. 7006 

 has the distinction of being the most remote celestial 

 object of which the distance has been determined 

 in a manner that inspires some confidence. Dr. Har- 

 low Shaplev and Miss B. \V. Mayberry contribute an 

 article on it in Proc. Nat. Acad. Sci., May, 1921. It 

 is on a line from a to 7 Delphini, prolonged to twice 

 the distance between them. The distance in kilo- 

 parsecs bj' five independent methods is given as 

 follows : — 



Distance Icp. MethoH. 



67 Parallax-diameter correlation. 



71 Photog. magnitude brightest 25 stars. 



62 Photo-vis. magnitude brightest 38 stars. 



63 Integrated visual magnitude. 



69 Median magnitude of 11 Cepheids. 



The mean of all the methods gives 664 kiloparsecs, 

 or 217 thousands of light-years. 



The first and fourth methods have little a priori 

 weight, and are merely used because experience shows 

 that the linear magnitudes and absolute luminosities 

 of globular clusters vary only between narrow limits. 



In the fifth method the measured median magnitude 

 is 18-96, and the assumed absolute magnitude is 

 — 0-23, derived from the study of similar stars in 

 other clusters. 



The assumption that there is no sensible absorption 

 of light in the intervening space is supported by the 

 fact that the colour indices of the brighter stars are 

 quite comparable with those of stars in the sun's neigh- 

 bourhood. Absorption would tend to make them 

 redder. 



