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Blondel as to the luminous intensity of flux,
illumination (_eclairement_), light (_eclat_), and lighting
(_eclairage_), with the corresponding units, decimal candle, _lumen_,
_lux_, carcel lamp, candle per square centimetre, and _lumen_-hour.[4]
[Footnote 4: These are the magnitudes and units adopted at the
International Congress of Electricians in 1904. For their definition
and explanation, see Demanet, _Notes de Physique Experimentale_
(Louvain, 1905), t. iv. p. 8.--ED.]

Sec. 7. MEASURE OF CERTAIN PHYSICAL CONSTANTS
The progress of metrology has led, as a consequence, to corresponding
progress in nearly all physical measurements, and particularly in the
measure of natural constants. Among these, the constant of gravitation
occupies a position quite apart from the importance and simplicity of
the physical law which defines it, as well as by its generality. Two
material particles are mutually attracted to each other by a force
directly proportional to the product of their mass, and inversely
proportional to the square of the distance between them.


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