JOHN’sS Way. 151 |

“Why, one day he was up in the second
story of the shop ,

‘Were there two stories?” asked Rollo.

“Yes; and in the second story there were
lathes, and various machines for finishing
off nice work, all carried by water. Well,
John was there seated before an emery-
wheel, brightening some screws that. were
going to be tempered.”

‘What does that mean?” asked Lucy.

“Why, you see when they want screws
to be hard, they temper them. First, they
heat them very hot, and put them in cold
water, and that makes them very hard and
brittle. Then, they heat them again a little,
not quite red hot, and plunge them into cold
water again, and that makes them not quite
so hard and brittle, but more tough; and
they have to brighten them a little before
they heat them the second time, in order to
know how hot to make them.”

“How do they know by that?” asked
Rollo.

“Why, if steel is bright,” said Jonas,
“and you heat it, it first turns straw-color,
then blue, and at last deep purple, as it