um."

They went down, wetted the sand, and ground away for fifteen minutes;
washed the glass, started again, and at the end of another fifteen
minutes went up to repeat the process of drawing off the thick water
into the basin. This was left to stand till evening, when the water was
poured back, and about a double quantity of thin paste to that obtained
in the morning placed in a size larger bottle, and labelled
"thirty-minute emery."

Again the whole was well stirred, and left for fifteen minutes; the
process repeated, and a much larger quantity obtained and bottled.

The next day the emery was stirred, and allowed to settle for five
minutes; then for two minutes, and the remainder bottled by itself, this
being by far the largest quantity, and in fact so much strong sharp
grit.

"There!" cried Uncle Richard; "now, going backwards, we have six
different grades of material, beginning with the coarse, and going up to
the fine sixty-minute powder or paste for polishing, for these things
have to be made exquisitely fine."

At the next attack upon the glass to dig it out into a hollow, the sand
was all carefully washed away, showing the disc to be thoroughly
scratched all over, and looking somewhat like the inside of a
ground-glass globe.

"So far so good, Tom," said Uncle Richard; "now let's try our mould."

He took down the convex-shaped piece of zinc, and placed it upon the
newly-ground-glass, into whose face it descended a little way, but only
a very little.

"Not deep enough yet, Tom," he said; "the mould ought to fit into it
exactly."

"Yes, I understand now," said Tom; "we have got to grind more out of the
middle."

"Exactly."

"Shall I fetch the sand back?"

"No, we will use the coarsest emery now; I dare say that will dig out
enough. Now then, number one."

The large-stoppered bottle was fetched from its shelf, and a small
portion of the most coarse ground emery taken out with a spatula, spread
upon the fixed glass, the speculum carefully laid upon it, and turned a
little to spread the material more equally, a few drops of water having
been added, and the slow, tedious grinding went on again.

"Hard work, my boy," said Uncle Richard, as they paused at last from
their laborious work, the disc they moved to and fro and round and
round, as they slowly changed their positions, being exceedingly heavy.

But Tom, as soon as he got his breath, was too much interested to mind
the labour, and after hel