led as if he understood the difficulty of rousing her
pupils' interest. This was somewhat embarrassing; but the school was
famous and visitors were now and then shown round.

She paused, and the stranger turned to the principal. "If you will allow
me--"

The principal smiled and he came up to Agatha, holding out his hand for
the chalk.

"Suppose we alter the formula this way?" he said and wiped out the
letters and figures.

Agatha studied him as he wrote fresh symbols. He was plainly dressed and
about sixty years of age. There was nothing else worth noting, but he
obviously knew his subject and she liked his face. She saw that the
girls could follow his explanation, but while suited to their
understanding, it was, in one respect, not quite accurate.

"I don't know if I've made it much plainer," he said deprecatingly when
he stopped.

Agatha indicated a group of letters. "It is plainer, thank you! But does
the combination of the two elements take place exactly as you have
shown? At a normal temperature, the metal's affinity for oxygen--"

"Ah," he said, "you know that? It looks as if you had studied the new
Austrian theory. But perhaps one may make a small concession, for the
sake of clearness."

"Science is exact," Agatha replied.

"It's a bold claim for us to make," he rejoined, smiling. "Our symbols
are guess measures; our elements split up into two or three. But I
gather that you refuse to compromise about what, in the meantime, we
think is the truth?"

"I think one must adhere to it, as far as one knows."

"Well, no doubt, that is the proper line. But I've stopped your lecture
and perhaps bored your pupils."

"No," said Agatha. "You have helped me over awkward ground, and I expect
they would sooner listen to a stranger."

He went away with the principal, and Agatha wondered about him as she
resumed her task. It was plain that he knew something about science, but
this was not strange, since geologists and chemists sometimes visited
the school. After she dismissed her class the principal sent for her.

"I suppose you don't know who that man is?" she asked.

Agatha admitted that she did not know and colored when the other told
her. The man was a famous scientist who had recently simplified the
smelting of some refractory British Columbian ores, and was now
understood to be occupied with the problem of utilizing certain barren
alkali belts in the West.

"Oh!" she said, "I talked to him as if he were