On the first evening, after camp had been pitched on the summit of the pass, he sat on a chunk of moss-covered granite, gazing meditatively into the glowing coals of a glorious fire. He imagined he had succeeded in banishing all thoughts of that desirable mountain-top from his mind, and yet, all of a sudden, he became aware that it was the very thing he was thinking of. He gave himself a petulant shake as he realized this, and was about to move away, when "Billy" Brackett, who sat on the end of a log near him, spoke up and said,
"Glen, how would you like to try a bit of mountain climbing with me to-morrow?"
"I'd like it better than anything I know of," answered the boy, eagerly.
"All right, it's a go, then; you see the chief is going off on an exploration with the topographer; and, as we can't run any lines till he comes back, he asked me if I'd take a couple of fellows and measure the height of that peak."
"Do you mean to chain from here away up there?" asked Glen, in astonishment, glancing dubiously up at the dim form towering above them.
"Chain! Not much, I don't!" laughed Brackett. "I mean carry up a barometer, and measure with it."
"How?" asked Glen, to whom this was a novel idea.
"Easy enough. We know that, roughly speaking, a barometer varies a little less than one tenth of an inch with every hundred feet of elevation. For instance, if it reads 21.22 where we now are, it will read 21.14 a hundred feet higher, or 20.40 at an elevation of a thousand feet above this. There are carefully prepared tables showing the exact figures."
"Can't you do it by boiling water, too?" asked Binney Gibbs, who had approached them unobserved, and was an interested listener of this explanation.
"Certainly you can," answered "Billy" Brackett, looking up with some surprise at the young scholar. "By boiling water we have a neat check on the barometer; for, on account of the rarefication of the air, water boils at one degree less of temperature for about every five hundred feet of elevation."