We are placed in a world of variable lights, of day and night, and of all the variations between light and darkness.

We can not see in the full blaze of light, nor yet in utter darkness.

Had the eye been formed to bear only the noonday glare, we had been half blind in the afternoon, and wholly so in the evening.

If the eye were formed so as to see at night, we had been helpless as owls in the day.

But the variations of light in the atmosphere may be in some measure compensated, as we know, by regulating the quantity admitted to our houses--shutting up the windows.
When we wish to regulate the admission of light to our rooms, we have recourse to various clumsy contrivances; paper blinds, perpetually tearing, sunblind rollers that will not roll, venetian blinds continually in need of mending, awnings blowing away with every storm, or shutters, which shut up and leave us in entire darkness.