Custom teaches us that glass will stand any amount of washing and wiping without injury, but the lesson is wrong. It may hold good of tumblers and beer bottles, but when we come to the finer quality of glass of which lenses are made, and to the more highly polished and more accurately finished surfaces which they must possess, we find that it is hardly an exag-gtion to say that we cannot touch the surface of the glass without permanently affecting it. Certainly a degree of roughness which is habitual in the cleansing of table glass would spell ruin to a lens in a very little while. Yet the writer has seen a photographer breathe on the glass of a costly anastigmat and give it a rub with the corner of a focussing cloth, with all the delicacy and care of a child cleaning a slate - but no more. Only two kinds of impurities should need removal from the lens - dust and grease.

Dust, and under this head we might include the dirt which may appear after a lens has got wet with rain or sea water, is best got rid of by a very gentle wipe with a piece of clean, washed cambric. Nothing is better for this purpose than an old handkerchief, washed out to remove laundry chemicals, and dried. Part of it should be dampened with clean water and the lens dabbed. In this way harsh particles of dustt and much dust is nothing but broken flint, are picked off instead of being ground round on the glass by rubbing. A gentle wipe with a dry part of the cloth completes the operation.

If the lens has got greasy from finger marks or otherwise, a little rectified benzine or ether may be applied to the handkerchief. Its surface must not be allowed to get quite wet with either because it might work into the cell and affect the cementing. The great thing is to remember that glass is easily injura-ble, and to act accordingly.-"Photography, " London.