It
will be found that a line joining the extremities of the strokes
are strictly parallel to the top or bottom and that they are not
on a slant at all. It is the slant of the numerous short lines
that go to make up the letter as a whole that deceives the eye.
[Illustration: Illusion]
** Home-Made Micrometer [130]
It often becomes necessary to find the thickness of material so
thin, or inconvenient to measure, that a rule or other measuring
device will not serve the purpose. A simple, fairly accurate, and
easily made apparatus of the micrometer form may be constructed as
shown by the accompanying sketch. Secure a common iron or brass
bolt about 1/4-in. in diameter and about 2-1/2 in. long, with as
fine a thread as possible, and the thread cut to within a short
distance of the head of the bolt. The head of the bolts should
have a slot cut for the use of a screwdriver. Clamp together two
blocks of wood with square corners which are about 1 in. wide, 3/4
in. thick and 2-1/2 in. long and fasten them together with small
pieces nailed across the ends. The width of the blocks will then
be about 2 in.
Pages:
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322