290 



THE POPULAR SCIENCE MONTHLY. 



are not determined by any law of Nature, but depend upon a particu- 

 lar collocation of matter. The same is the case with respect to the 

 size of the earth, from which the standard of what is called the metri- 

 cal system has been derived. But these astronomical and terrestrial 

 magnitudes are far inferior in scientific importance to that most funda- 

 mental of all standards which forms the base of the molecular system. 

 Natural causes, as we know, are at work, which tend to modify, if 

 they do not at length destroy, all the arrangements and dimensions 

 of the earth and the whole solar system. But though in the course 

 of ages catastrophes have occurred, and may yet occur, in the heavens, 

 though ancient s} 7 stems may be dissolved and new systems evolved 

 out of their ruins, the molecules out of which these systems are built — 

 the foundation-stones of the material universe — remain unbroken and 

 unworn. 



They continue this day as they were created, perfect in number, 

 and measure, and weight, and, from the ineffaceable characters im- 

 pressed on them, we may learn that those aspirations after accuracy 

 in measurement, truth in statement, and justice in action, which we 

 reckon among our noblest attributes as men, are ours, because they 

 are essential constituents of the image of Him who in the beginning 

 created, not only the heaven and the earth, but the materials of which 

 heaven and earth consist. 



Table of Molecular Data. 



Rank 



Rank 



( Mass of molecule (hydrogen = 1) 

 I. — 4 Velocity (of mean square), me- 





Rank III 



- 



tres per second at 0° C. 

 Mean path, tenth-metres. 

 Collisions in a second (millions). 

 Diameter, tenth-metre. 

 Mass, twenty-fifth grammes. 



Hydrogen. 



Oxygen. 



Carbonic 

 Oxide. 



1 



16 



14 



1,859 



465 



497 



965 



17,750 



5.8 



46 



560 



7,646 



7.6 



736 



482 



9,489 



8.3 



644 



Carbonic 

 Acid. 



22 

 396 



379 

 9,720 



9.3 

 1,012 



Table of Diffusion: (ceiltime f )2 



second 



-measure. 



H&O 



H&CO.... 



H&CO 2 .... 



O & CO 



& CO 2 

 CO & CO 2 . . . . 



H 



O 



CO 



CO 2 



Air 



Copper 



Iron 



Calculated. 



0.7086 

 0.6519 

 0.5575 

 0.1807 

 0.1427 

 0.1386 

 1.2990 

 0.1884 

 0.1748 

 0.1087 



Observed. 



Cane-sugar in water 

 Diffusion in a day 

 Salt in water 0, 



0.72141 



0.6422 



0.5558 



0.1802 



0.1409 



0.1406 



1.49 



0.213 



0.212 



0.117 



0.256 



1.077 



0.183 



00000365 



3114 



00000116 



Diffusion of matter observed by Loschmidt, 



Diffusion of momentum. 

 Graham and Meyer. 



Diffusion of temperature observed by Stefan. 



Voit. 

 Pick. 



