286 



NA TURE 



[January 22, 1903 



In 1S73, St was determined to omit the silver and to use only 

 copper as the alloying metal, hut Sir W. C. Roberts-Austen 

 expressed some doubts at the time whether plates consisting of 

 alloys of gold and copper were uniform in composition, and 

 proposed the use of trial plates of pure gold. There are, ' 



how- 



Fic. 1. — Alloy consisting of gold 91*0 jercenti, silver S'3 per cent. I .>-t t£oo, 



ever, objections to this method of procedure, and the law en- 

 joining the use of standard plates was not altered. 



In 1900, the authors of this paper showed that, as had been 

 feared, the gold copper alloys were not homogeneous (Roy. Soc. 

 Proc, vol. lxvii. , 1900, p. 105), and experiments on the gold- 

 silver series were then made. Cooling curves of the alloys 



Fig. 2.— Same as Fig. 



Annealed for two months, xisoa 



were taken by the Roberts-Austen recording pyrometer, with the 

 result that all the alloys were found to solidity without passing 

 through a pasty stage and no traces of a eutectic alloy were 

 observed. The first additions of silver to gold do not lower 

 its point of solidification, and the freezing-point curve was shown 

 to be horizontal in passing from pure gold to the alloy contain- 



NO. 1734, VOL. 67] 



ing 50 atoms of silver to 50 of gold. With further additions 

 of silver, there is a steadily increasing fall in the freezing point 

 until the lowest point is reached at pure silver. There is 

 accordingly no reason to suppose that, when alloys rich in gold 

 are allowed to c 0o l from a molten state, the first portion of metal 

 solidified would be different in compo- 

 sition from the mother liquor. 



The alloys all consist ot large grains 

 built up of minute secondaty crystals, 

 shown in Fig. 1, in which the alloy 

 containing 9i6'6 parts of gold and 833 

 of silver is shown under a magnification 

 of 1500 diameters. An ingot of this 

 composition was heated for two months 

 in an annealing furnace at a low red 

 heat, but although the size of the crystals 

 was greatly increased, as shown in Fig. 

 2, in which the magnification is the same 

 as in Fig. I, no true segregation could 

 be detected in the ingot either by assry 

 or with the aid of the microscope. Plates 

 prepared by rolling out ingots of standard 

 fineness were found on analysis to be 

 uniform in composition, and they have 

 been used throughout the year 1902 for 

 checks in the assay of standard bars and 

 coin. In view of the minute accuracy 

 with which the operations of coinage 

 have to be conducted, this is a matter 

 of much practical importance. 



Royal Astronomical Society, 

 January 9. — Dr. J. W. L. , Glaisher, 

 F.R.S., president, in the chair. — 

 Prof. H. H. Turner read a preli- 

 minary note by Mr. Bellamy and 

 himself on the possible existence 

 of two independent stellar systems. 

 The investigation described in a previous paper had been ex- 

 tended to the southern hemisphere and the number of stars in 

 each square degree had been counted ; the differences of dis- 

 tribution were apparently best explained by assuming the exist- 

 ence of a belt of stars. This seemed to point to the existence 

 of i»n .superposed stellar systems. It was proposed to make a 

 further study of the solar motion in 

 space, first Irom stars in the suggested 

 belt and then from stars in the Milky 

 Way.— Mr. A. R. Hinks read a paper 

 on a graphical method of applying to 

 photographic measures the terms of the 

 second order in the differential refrac- 

 tion. It appeared that Prof. Turner's 

 method of reducing measures in linear 

 coordinates had the advantage that the 

 small differences (refraction, sVc.) are 

 linear functions of the coordinates, but 

 the method loses its simplicity when 

 corrections involve terms of the second 

 order. A graphical method was sug- 

 gested for finding separately and apply- 

 ing to the measures such parts of the 

 reductions as are of the second order. 

 The author had succeeded in constiuct- 

 ing diagrams by means of which these 

 small terms can be quickly found for 

 any plate.— The secretary partly read a 

 paper by Mr. J. E. Gore on the sun's 

 stellar magnitude, obtained from a con- 

 sideration of binary stars the orbits of 

 which were well determined and the 

 spectra of which were of the solar type. 

 —The secretary also gave an account of 

 a paper which had been communicated by 

 the Astronomer Royal on statistics of 

 stats in a zone of 5°, from + 65° to 

 + 70' declination, counted on photographs taken for the 

 Astrographic Chart and Catalogue at the Royal Observatory, 

 Greenwich. The paper gave a comparison of the number 

 of stars for each square degree on the photographs with 

 those of the Bonn Durchmustetung, and an analysis of the 

 number of stars in each square degree in terms of duration of 



