It will be seen that this lower rate would bring the temperature of Mars at the equator down to 20 deg.

F.below the freezing point of water from this cause alone.
[Footnote 17: A four inches barometer is equivalent to a height of 40,000 feet above sea-level with us.] But all enquirers have admitted, that if conditions as to atmosphere were the same as on the earth, its greater distance from the sun would reduce the temperature to-31 deg.

F., equal to 63 deg.

below the freezing point.

It is therefore certain that the combined effect of both causes must bring the temperature of Mars down to at least 70 deg.