502 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The above is followed by a wbole page on " tbo Reflecting Micro- 

 scope," no sucb a Microscope having been made certainly since 1840. 



Micromillimetre.* — Prof. A. W. Riicker observing that tbo word 

 micromillimetro is used as equivalent to tbe thousandth of a millimetre, and 

 being told tbat it is now commonly employed by biologists, and especially 

 by botanists, witb tbat meaning, protests against sucb a use of tbe word. 



As ho thinks it would be very unfortunato if the same word were 

 habitually used in different senses by students of different branches of 

 science, he points out that, according to the definitions of the C.G.S. 

 system, a micromillimetre is the millionth of a millimetre. 



In tbo well-known report of the Committee of the British Association 

 for the " Selection and Nomenclature of Dynamical and Electrical 

 Units," it is laid down that the prefixes mega and micro are to be em- 

 ployed " for multiplication and division by a million." This ruling has 

 been generally accepted not only by scientific men, but also by those 

 engaged in commorce. Megohm and microfarad are terms which are used 

 in contracts, and are universally understood to mean a million ohms and 

 a millionth of a farad respectively. It will be hopeless, he thinks, to try 

 to introduce scientific systems of measurement into the affairs of daily 

 life if scientific men themselves disregard the rules on which those 

 systems are framed. 



It would also, in his view, be particularly confusing if the micro- 

 millimetre were wrongly used by microscopists. In its proper sense it 

 is the most convenient unit in which to express molecular magnitudes. 

 It has been employed for that purpose by Sir William Thomson and 

 others in England, and also by physicists abroad. If the micromillimetre 

 of the microscopist is 1000 times too large, all sorts of mistakes will be 

 rife as to the relative dimensions of molecules and of the smallest objects 

 visible with the Microscope. 



The proper name for the thousandth of a millimetre (/i.) is, in his 

 view, the micrometre, and though the similarity of this word to micrometer 

 is no doubt a drawback, it is not likely that confusion could often arise 

 between them. He therefore begs respectfully to suggest that botanists 

 should bring their nomenclature of units of length into conformity with 

 the definitions of the C.G.S. system. Otherwise there will be a permanent 

 confusion between the micrometre (/x) and the micromillimetre (fx/x). 



On the other hand, Mr. H. J. Chaney suggests | " that even the de- 

 nomination ' micrometre ' may be hardly acceptable to scientific workers. 

 The denomination for the measure of the one-thousandth of a millimetre 

 (li.), or 0*000001 metre, is 'micron,' and not 'micrometre.' 



" For the ' micron ' we have the authority of the ' Comite International 

 des Poids et Mesures.' One shudders at the thought of the confusion 

 likely to arise when computers are required to deal with both micro- 

 metre-units and micrometer-divisions. 



" The Comite International have also recommended the use of the 

 following metric denominations for minute measurements : — 



Equivalent. 

 .. 0-001 millimetre. 



0*001 milligramme. 

 .. 0-001 litre. 

 .. 0-000001 litre." 



" Nature, xxxvii. (1888) pp. 388-9. f Ibid., p. 138. 



