36 



originally conducted at the Mint, but since the establishment 

 of the Standards Department of the Board of Trade it has been 

 relegated to that Department. I was informed by Mr. 

 Chaney that sample coins are taken at haphazard from 

 coinings, and deposited in a strong room in the Pyx Tower ; 

 at the end of the year they are taken out and verified care- 

 fully ; by this means a check is maintained upon the accuracy 

 of the work at the Eoyal Mint. As a rule these trials prove 

 the errors, as to weight and fineness of the coins, to be far 

 within the allowed limits, and I doubt if any case of condemn- 

 ing has occurred within late years. G-lass weights are some- 

 times used by tradesmen to test gold coins. 



LIGHT. 



An Act of 1859 provides a standard of light, and modes and 

 apparatus for testing lights. In accordance with this the 

 necessary standard burners, photometer, &c, are deposited, 

 amongst other standards, with the Board of Trade. The drawing 

 in Plate XIII. will show one of the two authorised forms of pho- 

 tometers and the form of burner. The legal standard of light is 

 the sperm candle of six to the pound, burning 120 grains of 

 sperm per hour — the consumption of gas has to be adjusted to 

 five feet per hour. The candle has been proved to be a most 

 unsatisfactory standard, and there is at present a strong feeling 

 in favour of some other form being legalised. The opinions 

 lie between the Pentane standard of Vernon Harcourt and the 

 Methven slit, which are the chief competitors. 



Attention has lately been drawn to P. von Hefner Alteneck's 

 amylacetate lamp, the extreme variations of which are claimed 

 to lie within the limits of perception of the human eye, whereas 

 the candle (the existing standard) is liable to variations as 

 great as 23*7 per cent, in extreme cases, which would make 

 eighteen-candle gas appear to be either fourteen or twenty- two 

 candle power ; whereas the eye is, if properly assisted, capable 

 of judging to within about a fifth of a candle in eighteen- 

 candle gas (say about one per cent). 



Por cannel gas a burner specially constructed is legalised. 

 The Pentane standard of Vernon Harcourt consists in using 

 a specially-prepared gas from highly-rectified petroleum, 

 which, burned under certain fixed conditions, he claims, gives 

 a constant unit of light. John Methven's system is based on 

 the assumption that by cutting off from an ordinary argand 

 flame all but the central rays of light, by interposing a screen 

 having a slot of fixed size, a constant unit is thus obtained. I 

 found amongst authorities I met in England a very strong 

 feeling in favour of the latter ; and it is used at numerous 

 testing stations throughout England by Companies and Cor- 

 porations, but is not yet included in the British Standards. 



