204 



NATURE 



[June 30, 1887 



controversial point is conclusively dealt with. The writer 

 says : — " Again, though dimmed by heavy rain and thick 

 fog, as it has been during the last few nights, the triple 

 flash is always clear and unmistakable, and then produces, 

 through the quasi-opaque atmosphere, and at a distance 

 of thirty miles, the effect of the blurred disk of the moon 

 on a small scale. This remarkable penetration power of 

 the Tino light is conclusive proof, not only of how admir- 

 ably it is designed and suited to its essential purpose as a 

 guiding light under the peculiar atmospheric conditions of 

 the Mediterranean, but also how hazardous it would be to 

 dip — viz. to divert such a light, as has been suggested by 

 some — from the horizon to the nearer sea in foggy 

 weather, forsooth according to the bene placito of the 

 man in charge, on the presumption that in such weather 

 the luminous rays could not reach the horizon, and 

 would therefore be wasted. This presumption is wholly 

 fallacious in the Mediterranean, for in the Bay of Spezia, 

 owing to its proximity to the Apennines, the rainfall is 

 much greater than in other parts of the Tyrrhenean Sea, 

 and banks of land fog can often be seen hanging over the 

 bay and Tino, when the horizon as far as Leghorn, 

 Gorgona, and even Corsica, is perfectly clear.'' 

 June 1887. J. Kenward, 



REPORT OF THE BOARD OF TRADE ON 

 ? WEIGHTS AND MEASURES. 



/^NE of the many official Reports which are laid annually 

 ^^ before Parliament, but which unfortunately are not 

 so carefully read by the general public as they might be, 

 is a Report by the Board- of Trade on their proceedings 

 and business under the Weights and Measures Act of 

 1878. In Report No. 9, Sess. II., 1886, there is some- 

 thing of scientific interest to which we would invite the 

 attention of our readers. 



The only two units from which all Imperial measures 

 and weights are derived are, as is well known, the yard 

 and the pound, and material standards of these two units 

 are deposited with the Board of Trade. The Act pro- 

 vides that an accurate copy of each of these standards is 

 to be made, and an account of the verification of a new 

 copy of the yard measure is given in the present Report. 

 The results of the comparisons of the new yard, P.C. VI., 

 with the Imperial standard yard No. i, show that it differs 

 little from the original standard : — 



P.C, VI. = No. I — O'ooooo34 inch. / = 62° F. 



There are no two primary standards between which our 

 present scientific methods cannot measure some difference, 

 but the above two standards would appear to be as nearly 

 alike as it is possible to make them. 



In determining the rate of expansion by heat of the 

 new standard yard (which is a bronze bar 36 inches long), 

 it was found that with a rising temperature, the new bar 

 expanded o'ooo356 inch for 1° F., but with a falling tem- 

 perature it contracted at a lesser rate, o'ooo343 inch 

 for 1° F. It is not stated whether this curious differ- 

 ence in the rate of expansion, as determined when the 

 temperature is alternately rising and falling, is owing to the 

 march of the mercurial thermometers or to other causes. 

 Some doubt has arisen as to the rate of expansion of the 

 metal (bronze) of which the Imperial standard was made. 

 The thermometric expansions stated in the Report of the 

 Astronomer-Royal on the construction of the Imperial 

 standard {Phil. Trans. Roy. Soc, part iii., 1857, p. 61) do 

 not agree with those stated by Colonel Clarke and Sir 

 Henry James in their Report on the comparisons of 

 standards of length (1886). The actual rate of expansion 

 of the Imperial yard was, in fact, not determined by the 

 Standards Committee in 1857, but was assumed to be 

 the same as that of other similar bars of the same metal. 

 The more recent experience, however, is that no two 



bronze bars expand by heat at precisely the same rate, 

 although they may be of the same dimensions, form, and 

 material. The co-efficient of expansion of an alloy is 

 slightly affected by differences in the age of the alloy, by 

 its being subjected to extreme variations of heat and cold, 

 and by peculiarities in molecular condition. 



With reference to the metric system, we are glad to see 

 that during 1886 standards of metric weight and measure 

 were verified for certain authorities for use in scientific 

 research or otherwise. It would, however, appear that 

 in Japan, in the competition for commercial acceptance, 

 the British system is at present outstripping the metric 

 system. 



The legal equivalent of the metre is 39*37079 inches, 

 but, as some doubt has been expressed as to the scientific 

 accuracy of this equivalent. Prof. W. A. Rogers, of 

 Colby University, has undertaken to construct for the 

 Standards Department a subdivided standard yard and 

 metre, on which the precise length of the two standards 

 shall be marked off, so that an exact inter-comparison of 

 the two standards may, as far as practicable, hereafter be 

 made at London and at the Bureau International des 

 Poids et Mesures, at Paris. 



In this Report we have for the first time complete and 

 trustworthy information as to the standard weights and 

 measures in use in China and Japan, Her Majesty's 

 ministers at Pekin and Tokio having obtained the infor- 

 mation from the native Governments and through the 

 different local consuls. 



During the year 1886 the Standards Department 

 was specially engaged in the re-verification of the 

 accuracy of its own standards, and in the issue to 

 local authorities of some suggestions with reference to 

 the duties of inspectors of weights and measures. 

 Amongst the re-verifications particularly referred to we 

 notice a memorandum on the re-verification of the gas- 

 measuring standards, a memorandum which shows the 

 several conditions necessary for the accurate measure- 

 ment of gas used for lighting purposes. The accuracy of 

 the unit of volume, the cubic foot, is made to depend on 

 the Imperial standard pound, and not on linear measure- 

 ment. Experience has hitherto shown that the determina- 

 tion of the weight of a cubic foot of distilled water may 

 best be made by means of a round vessel which holds 

 a quantity of water equal to 62'32i lb. avoirdupois at 

 62° F., rather than by a vessel of rectangular shape, 

 which might be made to measure one foot in each of 

 its dimensions. In this memorandum reference also 

 is made to a slight difference in the methods of determin- 

 ing the zero, or freezing-points, of thermometers. It is, 

 for instance, uncertain how long a thermometer should 

 remain in melting ice or snow before its precise freezing- 

 point is noted. At the Bureau of Weights and Measures 

 at Paris, for instance, the thermometer is only left in the 

 pounded ice just long enough for it to reach the maximum 

 of depression. With thermometers made of hard glass 

 it is stated to be desirable not to hurry the observations — 

 the thermometers remaining long enough to allow the use 

 of a micrometer, and several observations to be taken ; 

 but with other kinds of glass it is found to be desir- 

 able to be as quick as possible. This practice is 

 also stated to be adopted at the Standards Offices at 

 Berlin and Washington. On the other hand, at Kew 

 the freezing-point of a thermometer is not observed 

 until the instrument has been completely buried, both 

 bulb and stem, up to 32° F., or 0° C, in well-pounded 

 block ice for a period of not less than a quarter of an 

 hour, care being always taken in cold weather to insure 

 the whole of the ice being in a melting condition during 

 the experiment by pouring a small quantity of tepid water 

 over it from time to time. 



Unlike the determinations of the rate of expansion of 

 gas, there has not been made any determination of the 

 rate of expansion of water which in exact experiments 



