The book of wonders : $b gives plain and simple answers to the thousands of everyday questions that are asked and which all should be able to, but cannot answer...
Science
The book of wonders : $b gives plain and simple answers to the thousands of everyday questions that are asked and which all should be able to, but cannot answer...
Curiosities and wonders; Encyclopedias and dictionaries; Questions and answers; Science -- Miscellanea; Technology -- Miscellanea
Man may never know how many stars there are. The best we can do is
to figure on the number that can be seen with the largest telescopes
which have been invented, for, of course, you know there must be many
millions of them which to us are invisible. We have counted the stars
so far as we can see them; or, rather, so far as we can photograph
them. Astronomers have found that a photographic plate exposed to the
stars will show more of them than can be seen by the naked eye. This
is because the materials on a photographic plate are more sensitive
to the light of the stars than the human eye. By this method man has
been able in a way to count the stars he can see. It adds up to more
than a hundred million of them. Astronomers found this out by taking
photographs of the heavens at night, devoting one picture to each
section, until the entire heavens had been covered, and then counting
them.
[Illustration: WHERE PAINT COMES FROM
MAKING LEAD BUCKLES--THE FIRST STEP IN PAINT MAKING.]
The Story in a Can of Paint
Paint such as is most frequently used is the material used for painting
buildings, such as houses, barns, stores, and many others which we need
not mention here. This paint is used on these buildings mostly for two
very important reasons--one being to beautify the buildings, the other
being to protect them from the ravages of the weather, much in the same
way that your clothes protect you from the weather.
Paint such as we mention here may be regarded as the most simple
and useful form. You have no doubt frequently seen the painter-man
spreading paint on some building, or perchance, you have seen your
father doing it, and have noticed that paint is a fluid substance
looking something like cream, which is applied to the surface to be
painted with a suitable brush and is brushed out smoothly. After the
first coat is dry, other coats are put on in the same way until enough
paint has been put on to thoroughly hide the unevenness of the lumber
and making it of a uniform color.
This paint is made by simply mixing together dry powder, which is
usually called pigment, with a thin, yellowish liquid which is called
linseed oil. In the earlier days, the painter-man mixed this paint
himself whenever he desired to use it. In these more modern times, he
usually buys this paint already prepared.
Perhaps a little history of the preparation of the package of a can of
paint which he buys may be interesting to you.
Let us imagine that the can of paint is white. In this case, the
pigment which is used is a white powder and is made of either metallic
lead or metallic zinc. The preparation of this fine white powder is
very interesting and requires considerable time to perfect.
Public-domain text, read in full here on John Shaqi.
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