1880.] 



MICROSCOPICAL JOURNAL. 



33 



l-300,000tli of an inch, and yet, 

 until now, we have made no rea- 

 sonable effort to free ourselves from 

 avoidable errors known to be many 

 times larger than that amount. 

 While coal at $4.00 a ton and mus- 

 lin at six cents a yard are, or at 

 least pretend to be, measured with 

 apparatus that has been carefully 

 verified by standards of known 

 quality, we have been measur- 

 ing spaces almost infinitesiin al- 

 ly small by standards of only 

 commercial quality and posses- 

 sed of manifest and uncorrected 

 errors. This fact is too suggestive 

 of the days when micrometers con- 

 sisted of grains of sand, and clip- 

 pings of wire ; with the odds 

 against us, that we know how to do 

 better. Arrange your microscope 

 so as to magnify 3,000 or 4,000 

 times, making the one-thousandth 

 of an inch on the stage seem three 

 or four inches long through the 

 lenses, then arrange an ocular mi- 

 crometer so that the magnified one- 

 thousandth of an inch shall be cov- 

 ered by, for instance, one hundred 

 divisions of the ocular scale, and 

 finally ascertain exactly liow many 

 of the one-thousandths of an inch 

 on that or any other plate will be 

 similarly measured by precisely the 

 same one-hundred divisions above 

 it. Judging from my experience 

 and that of others who have tried 

 the experiment, you will probably 

 find a perfectly measurable discrep- 

 ancy between the different spaces 

 of the same name ; so that even 

 your own measurements, with the 

 same apparatus, will not be com- 

 parable with each other unless, as 

 often done, you select some one 

 average s])ace as a basis of compar- 

 ison, and are careful to use only 

 that. Now we are trying to 

 ascertain which of these various 

 spaces is the correct one ; or if not 

 one is right, then to obtain one that 



shall be ; or if that cannot be done, 

 at least to determine a known error 

 from which we can compute defi- 

 nite results. This is not a question 

 of makers, or dealers, or trade 

 interests in any form, but of un- 

 inixed and independent science. 

 We are attempting to procure a 

 standard because we need it, and 

 we hope for the cordial assistance 

 of microscopists of really scientific 

 spirit in the difficult work of attain- 

 ing it, and in the almost equally 

 important task of bringing it into 

 general and respected use. I call this 

 a standard for convenience, and not 

 in a strict or ultimate sense. Strictly 

 it is only an authenticated copy of a 

 standard, or portion of a standard, 

 namely, of the world's standard 

 meter or standard yard ; and hence 

 the importance, not fully shared 

 by the original meter itself, of its 

 corresponding perfectly with its 

 theoretical length. 



" The adoption of the metric 

 system has a formal sound, and its 

 difficulties have been, to say the 

 least, well represented. But, to 

 the extent of its use in micrometry, 

 it really presents no difliculties and 

 many advantages. The value of 

 the millimeter and its decimals 

 must be made familiar to the mind 

 for other purposes, even for the 

 understanding of exclusively En- 

 glish literature, and to use it for 

 our own measurements and state- 

 ments will merely assist to keep it 

 fresh in mind. The English sys- 

 tem, or rather tradition, presents 

 no pair of units so convenient for 

 the microscopist as the millimeter 

 for large objects and the 1-lOOOth 

 millimeter for small ones. For the 

 purposes of most people, for use in 

 micrometry alone, it is sufficient 

 to remember that the millimeter 

 is about one-twenty-fifth of an 

 inch, and surely that is no great 

 intellectual task. Nor would it 



