NA TURE 



29 



SATURDAY, JULY 8, 1922. 



CONTENTS. 



By R. J. T. 



PAGE 

 29 



Metric and British Measures 



Influenza .... 



History of Electrotherapy 



Mustard Gas Poisoning. By Prof. C. Lovatt Evans 



Tinctorial Chemistry and Histology. By Dr. M 



Nierenstein 



Mineral Resources of Yugoslavia. By H. L. . 



Hydraulics. By F. C. L 



Our Bookshelf . 



Letters to the Editor : — ■ 



The Difference between Series Spectra of Isotopes. — 



Prof. J. W. Nicholson, F.R.S. . 



A Possible Reconciliation of the Atomic Models of 



Bohn and of Lewis and Langmuir. — W. Hughes 



The Intensity of X-ray Reflection from Powdered 



Crystals. — Prof. A. H. Compton and Newell L. 



Freeman 



Discoveries in Tropical Medicine. — Sir Ronald 



Ross, K.C.B., F.R.S 



The Oldest known Rocks of the Earth's Crust. — 



Prof. Grenville A. J. Cole, F.R.S. . 

 An Exception to the Principle of Selection in Spectra. 



— S. Datta 39 



The Melbourne University Bill. — Sir. J. H. 

 MacFarland ....... 39 



Ball Lightning. —Prof. J. B. Cleland ... 40 

 Ouramoeba. — F. R. Rowley ; R. Kirkpatrick . 40 

 The Elliptic Logarithmic Spiral. — C. E. Wright . 40 

 Seasonal Incidence of the Births of Eminent People. 



—Dr. F. J. Allen 40 



The Paris and Liege Meetings of the Institution of 

 Mechanical Engineers ...... 41 



Absolute Measurements of Sound. [Illustrated.) By 



Dr. Arthur Gordon Webster 42 



Biological Studies in Madeira. By Dr. Michael 

 Grabham ......... 45 



Ten Years of X-ray Crystal Analysis. By Dr. A. E. 



H. Tutton, F.R.S 47 



Obituary 48 



Current Topics and Events 50 



Our Astronomical Column 53 



Research Items 54 



Coral Reefs of the Louisiade Archipelago. By Prof. 



W. M. Davis 56 



Root Respiration. By W. E. B 58 



Radio Direction Finding in Flying Machines . 59 



Industrial Research in India 59 



Rainfall in Southern Italy and Tripoli ... 60 

 University and Educational Intelligence ... 60 



Calendar of Industrial Pioneers 61 



Societies and Academies 62 



Official Publications Received— Diary of Societies . 64 



37 



37 



39 



Editorial and Publishing Offices : 



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ST. MARTIN'S STREET. LONDON. W.C.2. 



Advertisements and business letters should be 



addressed to the Publishers. 



Editorial communications to the Editor. 



Telegraphic Address : PHUS1S. LONDON. 

 Telephone Number : GERRARD 8830. 



Metric and British Measures. 



IN view of the vigorous and sustained efforts of 

 the exponents of the metric system, and the 

 eminent names that are to be found among them, 

 it is perhaps not a little surprising that it makes so 

 little progress towards general acceptance in Great 

 Britain. The Weights and Measures Act of 1897 

 legalised the metric denominations for use in trade, 

 and was expected to lead to its advantages being so 

 generally recognised that the Imperial system would 

 soon disappear. Twenty-five years have now elapsed, 

 and the position is almost unchanged. In fact, the 

 policy of compulsory introduction of the metric system 

 by law, which formerly was always strongly supported, 

 was ruled out by the Metric Committee of the Conjoint 

 Board of Scientific Societies in its Report in 1919, and 

 though the report of this Committee was not adopted 

 by the Board, the subject of compulsion is not likely 

 again to be seriously considered for some time at least. 

 Even the Decimal Association has recognised this 

 position, and now advocates a modification of the 

 Imperial system which will serve as a first step towards 

 facilitating the ultimate end it has in view. A modi- 

 fication of some sort is now being called for with 

 increasing insistence, so that it may be desirable to 

 examine the principal considerations involved. 



A fundamental distinction must, at the very outset, 

 be drawn between the importance of stability in the 

 units of quantity and of dimension respectively. The 

 units of mass and capacity, speaking generally, serve 

 simply for determining a certain quantity of goods, 

 and the margin of tolerance is usually fairly large ; 

 and even if this margin is greatly exceeded, the loss, 

 to one or the other party to the transaction, is 

 the value represented by the amount of the error alone. 

 An alteration in the magnitude of these units, there- 

 fore, if not very large, would pass almost unnoticed. 

 Material weights, and to a certain extent measures 

 also, can be adjusted without any great difficulty, 

 though the recalibration of weighing machines would 

 not be quite so simple. The unit of length is of a 

 different character. Size, which determines the inter- 

 changeability of parts and fittings, is not capable of 

 ready adjustment, and an error in dimensions often 

 involves the waste of the whole article. A change 

 from one unit to another, not commensurable with it, 

 must therefore introduce serious difficulty, in that 

 apparatus designed to suit one unit cannot easily be 

 adapted to be of service under the other. The only 

 kind of change which could be accepted without much 

 inconvenience would be one which left the new unit 

 expressible, in the terms of the old, by a simple ratio, 

 the absolute change of magnitude being of minor 



NO. 2749, VOL. I io] 



