Tom kept his word, for he started into wakefulness in the grey dawn out
of an uncomfortable dream, in which he had seen the unfinished speculum
fall off the bench on to the stone-floor, roll like a wheel out of the
door, down the slope to the gate, bound over, and then go spinning down
the lane and across the green, straight for the ragstone churchyard
wall, where it was shivered to pieces.
"Only a dream," he said, as he leaped out of bed, ran to the window, and
saw by the church clock that it was only half-past four.
"Time to go over and see if it is all right," he said, as he finished
dressing, "and then come back and call uncle."
Going down-stairs, he took the keys of the mill from where they hung by
the front door, went out into the garden, unlocked the gate, and went
across to the mill, where, on peering through the window, he could see
the glass lying just as it had been left.
"That's all right," said Tom; and he walked round by the back of the
tower to see how the flowers and shrubs looked, when, to his startled
surprise, he found footprints made by a heavy, clumsy pair of boots on
the border beneath the wall.
Their meaning was plain enough. Some one had walked along there, and
got out of the yard over the wall, while, upon a little further search,
he found the spot where whoever it was had entered the yard by jumping
down, the prints of two heels being deeply-marked in the newly-dug
earth.
"That must have been Pete," said Tom, flushing; and he looked over the
wall, half expecting to see the slouching figure of the lad.
But there was no one within sight, and he looked round the yard in
search of the visitor's object. There was nothing but the old
millstones stealable, and they stood here and there where they had been
leaned against tower and wall; and at ten minutes to five, after noting
that the sun was shining brightly, Sam went back to his uncle and called
him, and at half-past five they went together to the mill-yard, where
the footprints were pointed out.
"Have to keep the door carefully locked, Tom," said Uncle Richard.
"Hah! capital! the sun will be shining right through that window in a
few minutes."
They entered the workshop, where a bench was drawn opposite to the last
window, and about twelve feet away. To this, with Tom's help, the
partly-polished speculum was borne.
"Not very bright for a reflector, Tom," said Uncle Richard. "What am I
to do to make it brighter?"
"Go on polishing, uncle."
"Ah, but I want to test it this morning, to see if we have a good
curve," said Tom's elder, smiling. "Fill the sponge with clean water
and bring it here."
This was done, and the finely-ground surface was freely wetted, with the
effect that it became far more luminous directly.
"Now, Tom," said his uncle, "I'm going to show you something in
reflection. The sun is not quite high enough for the speculum, so give
me that piece of looking-glass."
This was handed to him, and he held it on high, so that the low-down sun
shone into it, and a reflection was cast from it back upon the wall just
above the window.
"See that?"
"Yes, uncle. Done that many a time. Used to call it making
jack-o'-lanterns."
"Well, that is the effect of a reflection from a flat or plane surface;
the rays of light strike back at the same angle as they hit the surface.
Now then, I'll show you what happens from a curved surface."
He passed the sponge rapidly over the ground speculum again, so as to
glaze it--so to speak--with water, raised it upon its edge with the
carefully-ground face directed at the window just as the sun rose high
enough to shine in; and then by turning the great mirror slightly, the
light reflected from it struck upon the wall at the side of the window.
"Now, Tom, what do you see?"
"A round spot of light about as big as a two-shilling piece," said the
boy.
"Yes; all the rays of light which fall upon our mirror, gradually drawn
together to where they form an image of the sun. It is only dull, my
boy, but so far finely perfect, and we can say that we have gone on very
successfully."
As he spoke he laid the mirror down upon its back.
"Is that all you are going to do?" asked Tom.
"Yes; I can test it no better till it is more advanced, my boy. It may
seem a little thing to you, but it is enough to show me that we may go
on, and not begin our work all over again. Now for a good turn until
breakfast-time. Two good hours' work ought to produce some effect."
The lower disc, now become convex, was wetted and lightly touched over
with number five emery, which seemed soft enough for anything; the
well-advanced mirror was turned over upon it, fitting now very closely,
and with the sweet morning air floating in from the pine-woods, and the
birds singing all around, the monotonous task went on with its
intermissions till Uncle Richard gave the final wash off, and
said--"Breakfast!"
They were so far advanced now that Tom was as eager to recommence as his
uncle, and by that evening so much progress had been made that the
setting sun was made to shine in upon it, to be reflected back in a
bright spot on the wall without the aid of water; while two evenings
later, when the great round glass was stood all dry the polish upon it
was limpid, and seemed to be as pure as could be. There was not the
faintest scratch visible, and Tom cried in triumph--
"There, now it is done! Oh, uncle, it is grand!"
"Grand enough so far, my boy. We have succeeded almost beyond my
expectations; but that is only the first stage."
"First--stage?" faltered Tom, looking at his uncle aghast.
"Yes, boy; we have succeeded in making a beautiful spherical concave
mirror, which could be of no use whatever for my purpose."
"Then why did we make it?" cried Tom. "For practice?"
"No, boy; because it is the step towards making an ellipse, or, as they
call it when shaped for a reflecting telescope, a parabola. You know
what an ellipse is?"
"Gooseberry," said Tom bluntly.
"Gooseberry-shaped," said his uncle. "Well then, what is a parabola?"
"One of those things we used to learn about in geometry."
"Good. Well, to-morrow we must begin polishing, or rather I must, to
turn our glass from a spherical-curved mirror into a parabola."
"You'll let me help, uncle?"
"As much as I can, my boy; but the amount I have to polish off, in what
is called figuring, is so small that it requires the most delicate of
treatment, and first of all we have to prepare a small polisher to work
by hand."
This was formed of lead in the course of the next day--a nearly flat but
slightly convex disc, with a handle upon its back, and when made
perfectly smooth it was covered with hot pitch, which, as it cooled, was
made to take the exact curve of the nearly finished mirror, by being
pressed upon it, the pitch yielding sufficiently for the purpose.
This done the pitch was scored across and across, till it was divided
into squares, with little channels between them, so that the polishing
powder and water might run freely between; then a final pressure was
given upon the mirror and the implement was left to harden till the next
day.
"Now for a few hours' polishing," said Uncle Richard the next morning,
as he took up the curved pitch tool and moistened it, no longer with
emery, but with fine moistened rouge; "and if I am successful in
slightly graduating off the sides here, and flattening them in an
infinitesimal degree, we shall have a good reflector for our future
work."
But upon testing it the result that evening was not considered
satisfactory. There were several zones to be corrected.
It was the same the next day, and the next. But on the fourth Uncle
Richard cried "Hold: enough! I think that is as good as an amateur can
make a speculum, and we'll be content."
That night Tom slept so soundly that he did not dream till morning, and
then it was of the sun resenting being looked at, and burning his cheek,
which possessed some fact, for the blind was a little drawn on one side,
and the bright rays were full upon his face.
"All that time spent in making the reflector!" thought Tom; "and all
that work. I wonder what the next bit will be."