the end of a quarter of an hour they arrived at the startling
conclusion that they had travelled perhaps many miles out of their way.
The metal of the weapons Jack carried having, as they saw only too
clearly now, deflected the needle.

"What an idiot I was not to think of such a possibility!" exclaimed
Jack bitterly.

"Not at all, my boy," comforted the professor. "The same thing has
happened to experienced sea-captains, and they have navigated many
miles off their course before they discovered their error."

"All of which, not bein' at' sea, don't help us any," grunted Pete.
"Suppose now, perfusser, that you jes' figger out as well as you kin,
how far wrong we hev gone."

"It will be a difficult task, I fear," said the professor.

"It'll be a heap difficulter task, ef we don't hit water purty soon,"
retorted the cow-puncher.

Thus admonished, Professor Wintergreen divested himself of his weapons,
and, taking out a small notebook, began, with the compass before him,
to make some calculations. At the end of ten minutes or so, he raised
his head.

"Well?" asked Jack eagerly.

"Well," rejoined the professor, "it's not as bad as it might be. We
are, according to my reckoning, about twenty-five miles farther to the
south than we should be."

He consulted his notebook once more.

"The bearings of the mesa require us to travel in that direction." He
indicated a point to the northward of where they were halted.

"And it's twenty-five miles, you say?" asked Pete.

"About that. It may be more, and again it may be less."

"Waal, the less it is, ther better it'll suit yours truly. This stock
is jes' about tuckered."

With the professor now bearing the compass, they set out once more,
this time taking the direction indicated by the man of science.

"Suppose the professor is wrong?" Ralph whispered to Jack, as they
urged their almost exhausted cayuses onward.

Jack shrugged his shoulders.

"What's the use of supposing?" he said.

It was sun-down, and a welcome coolness had begun to be noticeable in
the air, when Jack gave a shout and pointed directly ahead of them.

"Look, look!" he cried. "What's that?"

"That" was only a small purplish speck on the far horizon, but it broke
the monotony of the sky-line sharply. Coyote Pete scrutinized it with
keen eyes for a moment, narrowing his optics till they were mere slits.
Then--

"Give me the glasses, perfusser," he requested. Every one in the party
kn