Micrographia - Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon by Robert Hooke
page 113 of 465 (24%)
page 113 of 465 (24%)
![]() | ![]() |
|
The Seventh and last therefore that I shall prove, is, _That the gradual heating and cooling of these so extended bodies does reduce the parts of the Glass to a looser and softer temper_. And this I found by heating them, and keeping them for a prety while very red hot in a fire; for thereby I found them to grow a little lighter, and the small Stems to be very easily broken and snapt any where, without at all making the drop fly; whereas before they were so exceeding hard, that they could not be broken without much difficulty; and upon their breaking the whole drop would fly in pieces with very great violence. The Reason of which last seems to be, that the leisurely heating and cooling of the parts does not only wast some part of the Glass it self, but ranges all the parts into a better order, and gives each Particle an opportunity of _relaxing_ its self, and consequently neither will the parts hold so strongly together as before, nor be so difficult to be broken: The parts now more easily yielding, nor will the other parts fly in pieces, because the parts have no bended Springs. The _relaxation_ also in the temper of hardned Steel, and hammered Metals, by nealing them in the fire, seems to proceed from much the same cause. For both by quenching suddenly such Metals as have _vitrifed_ parts interspers'd, as Steel has, and by hammering of other kinds that do not so much abound with them, as Silver Brass, &c. the parts are put into and detained in a bended posture, which by the agitation of Heat are shaken, and loosened, and suffered to unbend themselves. * * * * * Observ. VIII. _Of the fiery Sparks struck from a Flint or Steel._ It is a very common Experiment, by striking with a Flint against a Steel, |
|