Refragability

However, as the reflecting telescope is essentially free from aberration of refragability, as the purity of its images depends only on the perfection of a single surface, […]

[…] that the rays emitted by solids at low temperature are invisible, but become red at 977° Fahrenheit, and augment in intensity, number and refragability at higher temperatures.

Yet, we know that, besides those radiations which give us the sensation of light, there are others, in endless series, both higher and lower in their refragability, to which our eyes are absolutely blind.