best illustrates the subject of maintaining true wearing surfaces, I
will leave it until I reach that part of my paper.

(_To be continued._)

* * * * *

THE MECHANICS OF A LIQUID.

A liquid comes in handy sometimes in measuring the volume of a
substance where the length, breadth, and thickness is difficult to get
at. It is a very simple operation, only requiring the material to be
plunged under water and measure the amount of displacement by giving
close attention to the overflow. It is a process that was first
brought into use in the days when jewelers and silversmiths were
inclined to be a little dishonest and to make the most of their
earnings out of the rule of their country. If we remember rightly, the
voice of some one crying "Eureka" was heard about that time from
somebody who had been taking a bath up in the country some two miles
from home. Tradition would have us believe that the inventor left for
the patent office long before his bathing exercises were half through
with, and that he did the most of his traveling at a lively rate while
on foot, but it is more reasonable to suppose that bath tubs were in
use in those days, and that he noticed, as every good philosopher
should, that his bathing solution was running over the edge of the tub
as fast as his body sunk below the surface. Taking to the heels is
something that we hear of even at this late day.

[Illustration]

It was not many years ago that an inventor of a siphon noticed how
water could be drawn up hill with a lamp wick, and the thought struck
him that with a soaking arrangement of this kind in one leg of the
siphon a flow of water could be obtained that would always be kept in
motion. Without taking a second thought he dropped his work in the hay
field, and ran all the way to London, a distance of twenty miles, to
lay his scheme before a learned man of science. He must have felt like
being carried home on a stretcher when he learned that a performance
of this kind was a failure. Among the others who have given an
exhibition of this kind we notice an observer who was more successful.
Being an overseer in a cotton mill, he had only to run over to his
dining room and secure two empty fruit jars and pipe them up, as
shown. He had had trouble in measuring volume by the liquid process by
having everything he attempted to measure get a thorough wetting, and
there were many substances that were to be experimen