Here we have somebody's 'estimate' quoted, there another person's 'observation,' and these are adopted without further remark and used in the various calculations leading to the result above quoted.

It requires a practised mathematician, and one fully acquainted with the extensive literature of this subject, to examine these various data, and track them through the maze of formulae and figures so as to determine to what extent they affect the final result.
There is however one curious oversight which I must refer to, as it is a point to which I have given much attention.

Not only does Mr.Lowell assume, as in his book, that the 'snows' of Mars consist of frozen water, and that therefore there _is_ water on its surface and water-vapour in its atmosphere, not only does he ignore altogether Dr.
Johnstone Stoney's calculations with regard to it, which I have already referred to, but he uses terms that imply that water-vapour is one of the heavier components of our atmosphere.

The passage is at p.

168 of the _Philosophical Magazine._ After stating that, owing to the very small barometric pressure in Mars, water would boil at 110 deg.