Page:The Solar System - Six Lectures - Lowell.djvu/69

Mars

51

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The number of molecules traveling at speed u is given by the equation,—

$\textstyle N{\sqrt {\frac {km}{\pi }}}e^{-kmu^{2}}du=dy$

just as the probability of an error is given by the equation,

$y={\frac {h}{\sqrt {\pi }}}e^{-h^{2}x^{2}}.$

VALUES OF THE SPEEDS.

G = mean value of speed in metres per second.
G'= mean value of speed in miles per second.

Hydrogen		.	.	.	.	.	1838	1.14
Water vapor		.	.	.	.	.	614	0.38
Nitrogen		.	.	.	.	.	492	0.31
Atmospheric air			.	.	.	.	485	0.30
Oxygen	.	.	.	.	.	.	461	0.29
Carbon dioxide			.	.	.	.	392	0.24
Cyanogen		.	.	.	.	.	361	0.22

These speeds are got from the consideration that the energy, from which follows the temperature, is the same in the two gases; and, therefore, that

$\textstyle {\frac {1}{2}}mv^{2}={\frac {1}{2}}m_{1}v_{1}^{2};$

and, therefore, the speed of the molecule is inversely as the square root of the atomic weight.

Air on Mars.

So far theory. Now it is not a little interesting that observation supports this. That air still exists on Mars, oxygen, nitrogen, and carbonic acid,