then he glanced at his watch.

"Is that scum the elutriation?" said Tom, with a faint grin.

"No, boy, the impurity; throw it down the sink. Now, Tom, we want to
get our finest polishing emery out of that mixture, and it will take an
hour to form--sixty-minute emery, the opticians call it; so while it is
preparing, we'll go and have another turn at the speculum."

They descended, leaving the pan standing on the heavy table, and after
spreading wet sand upon the lower disc of glass, the loose one was once
more set in motion, and uncle and nephew, with quarter-hour rests for
examination and wetting the surfaces, patiently ground away for an hour,
by which time, upon the speculum being sponged, it was found that the
greater part of the upper glass was deeply scratched.

"This is going to be an awfully long job," thought Tom.

"Yes, it is," said his uncle, who aptly read his thoughts, "a very long
job, Tom; but good things have to be worked for, boy."

"Oh, I'm not going to be tired, uncle. It's like working for a grand
prize."

"It is. Now then, let's see to the emery. Our finest must be ready by
now. Now I want all the water, from which the emery has settled down to
the bottom, drawn off into that great white basin. How is it to be
done?"

"Pour it off," said Tom.

"No; couldn't be done without disturbing the bottom. Let's try
syphoning."

Uncle Richard placed the basin upon a stool below the level of the
table, took up a glass tube bent somewhat in the shape of a long-shanked
hook, placed the short end gently beneath the surface of the nearly
clear water, his lips to the long end, drew out the air, and the water
followed directly from the atmospheric pressure, and ran swiftly into
the basin.

As it ran, and Tom watched, Uncle Richard carefully held the short arm
of the syphon, guiding it till the sediment at the bottom of the pan was
nearly reached, when he quickly withdrew it, and the basin was then
placed beside the pan.

"There, Tom," said Uncle Richard, "that's our sixty-minute emery."

"But I thought you said you wanted it very fine. You've only washed
it."

"We're playing at cross purposes, Tom," said Uncle Richard. "You are
talking about the contents of the pan, I about those of the basin."

"What! the clear water--at least nearly clear?"

"Ah, there you have hit it, boy--nearly clear. That water contains our
finest polishing powder, and it will have to stand till to-morrow to
settle