Spectacles for travelling by rail-road, on the old beaten path, or by vessels, are usually fitted with parallel glasses, unless the wearer requires focal power as well as a screen, in which case they are of the concave or convex figure, before explained. Almost every combination of light and shade has been used for this class of spectacles; violet, grey, blue, green, crape, wove wire, &c.; but some sensitive and tender eyes failed to receive the relief expected from any of these, and opticians have been repeatedly baffled in their attempts to produce a shade of glass congenial to the requirements of the eye under such circumstances. I have made extensive use of the new neutral tint, or twilight tinge glass, and find it most agreeable to the eye while employing it, and when removed, it leaves the vision undisturbed by the flickering and confused halo so much complained of after wearing other coloured glasses. The cause of this superiority is clearly seen when we remember that, after taking off a pair of green glass spectacles, every object appears of a red colour, while, upon the removal of blue colours, an orange or yellow mantle seems to rest on all which meets the view. It is of consequence that all such glasses should be really parallel, otherwise a broken and disjointed appearance will be given to objects, the rays of light being abruptly dispersed instead of being transmitted through the transparent medium to the eye, in their natural direction. I have always discountenanced the use of wire, gauze, crape, and muslin substitutes for glass, because, in my opinion, it is a fallacy to assert that they are cooler and more agreeable to the eye. There is abundant space for the circulation of air in the region of the eye if the spectacle-frame adapts itself pleasantly to the wearer’s face; while the eye and common sense may answer together, that to look on things around us, a transparent medium is preferable to a hazy and indistinct one. We do not choose bars and gratings, or coarse curtains, in preference to glass, for the windows of apartments; but if the light is sometimes too intense, we place a shade to soften its dazzling effects. Such precisely is the reason why tinted glass spectacles, for defending the eyes from rain, dust, and wind, are recommended. Lenses worked by machinery are produced in greater quantities, within a given time, than those worked by hand. They are passed through the different stages of grinding and polishing without having the keen eye of the workman carefully watching their progress, and adjusting the inequalities in their surfaces or edges, which will always appear more or less in the course of working.