Sronseyv— The known part of Nature's Work. 85 
see clearly where our knowledge must end, and to have ascertained 
definitely which part of the boundless range of Nature’s actual 
operations is that which human powers are able to gauge and 
which human minds can adequately grasp. The survey may be 
rendered definite with the help of the table comprised in fig. 6, 
in which numerical digits are to take the place of some of the 
ciphers. According to the place where we insert these numbers 
we can make them express by how many metres, or by what frac- 
tion of a metre, we are to measure any of the magnitudes with 
which man has become acquainted throughout the whole range of 
his study of Nature. 
In this table metros mean decimal multiples of the metre ; 
metrets mean its decimal sub-multiples; and kilem (to be pro- 
nounced with the 7 long’, as in mi/e) is used as convenient Hnglish 
- for the French “ kilométre.”’ The first few places in the table and 
the last four or five lie beyond the range of our present knowledge. 
Nevertheless they are included; in order that the table may not 
be unduly shortened by temporary ignorance on our part, but may 
provide a large margin for possible future discoveries. 
The significance of the survey is best appreciated by examining 
separately the four groups into which the table is divided, and it is 
convenient to begin with Group C, as it includes the measures most 
familiar to us. 
Group C (Lasoratory MEAsuRsEs). 
Group C extends from kilems (kilométres) on the left down 
to tenths of a micron on the right. The central sub-section v 
includes the measures most in use in our laboratories, from metres 
down to tenths of a millim or millimétre. Sub-section w includes 
those larger measures which men have also in every-day use——from 
tenths of a metre up to kilems or kilométres. ‘The third sub-sec- 
tion w, from millims (millimétres) down to tenths of a micron, 
covers the entire range of the microscope, and indeed travels somewhat 
beyond the grasp of that instrument, since the smallest interval at 
which two objects can be seen as two by the best immersion 
objectives supplemented by the best immersion condensers, and 
most carefully handled, is but little less than two tenths of a micron 
1Tn xiArds, ‘a thousand,’ and in all Greek words derived from xiArds, the ¢ is long. 
