Note A — THE RADIOMETER:

As some of the readers of this volume may be interested to compare these values, we reproduce the "Table of Molecular Data" from Professor Clerk Maxwell's lecture on "Molecules," delivered before the British Association at Bradford, and published in "Nature," September 25, 1873.

Molecular Magnitudes at Standard Temperature and Pressure, 0° C. and 76 c. m.

RANK ACCORDING TO ACCURACY OF KNOWLEDGE.Hydrogen.Oxygen.Carbonic Oxide.Carbonic Dioxide.

Rank I.

Relative mass 1 16 14 22

Velocity in metres per second 1,859 465 497 396

Rank II.

Mean path in ten billionths (10^-10) of a metre 965 560 482 379

Collisions each second—number of millions 17,750 7,646 9,489 9,720

Rank III.

Diameter in hundred billionths (10^-11) of a metre 58 76 83 93

Mass in ten million million million millionths (10^-25) of a gramme 46 736 644 1,012

Number of molecules in one cubic centimetre of every gas is nineteen million million million on 19 (10¹⁸).

Two million hydrogen molecules side by side measure a little over one millimetre.