matter is produced, and at length a soil is formed, in which grass can fix its roots.  In the crevices of walls, where this soil is washed down, even the seeds of trees grow, and, gradually as a building becomes more ruined, ivy and other parasitical plants cover it.  Even the animal creation lends its aid in the process of destruction when man no longer labours for the conservation of his works.  The fox burrows amongst ruins, bats and birds nestle in the cavities in walls, the snake and the lizard likewise make them their habitation.  Insects act upon a smaller scale, but by their united energies sometimes produce great effect; the ant, by establishing her colony and forming her magazines, often saps the foundations of the strongest buildings, and the most insignificant creatures triumph, as it were, over the grandest works of man.  Add to these sure and slow operations the devastations of war, the effects of the destructive zeal of bigotry, the predatory fury of barbarians seeking for concealed wealth under the foundations of buildings, and tearing from them every metallic substance, and it is rather to be wondered that any of the works of the great nations of antiquity are still in existence.

Phil.—­Your view of the causes of devastation really is a melancholy one.  Nor do I see any remedy; the most important causes will always operate.  Yet, supposing the constant existence of a highly civilised people, the ravages of time might be repaired, and by defending the finest works of art from the external atmosphere, their changes would be scarcely perceptible.

Eub.—­I doubt much whether it is for the interests of a people that its public works should be of a durable kind.  One of the great causes of the decline of the Roman Empire was that the people of the Republic and of the first empire left nothing for their posterity to do; aqueducts, temples, forums, everything was supplied, and there were no objects to awaken activity, no necessity to stimulate their inventive faculties, and hardly any wants to call forth their industry.

The Unknown.—­At least, you must allow the importance of preserving objects of the fine arts.  Almost everything we have worthy of admiration is owing to what has been preserved from the Greek school, and the nations who have not possessed these works or models have made little or no progress towards perfection.  Nor does it seem that a mere imitation of Nature is sufficient to produce the beautiful or perfect; but the climate, the manners, customs, and dress of the people, its genius and taste, all co-operate.  Such principles of conservation as Philalethes has referred to are obvious.  No works of excellence ought to be exposed to the atmosphere, and it is a great object to preserve them in apartments of equable temperature and extremely dry.  The roofs of magnificent buildings should be of materials not likely to be dissolved by water or changed by air.  Many electrical conductors should be placed so as to prevent the slow or the rapid effects of atmospheric electricity.  In painting, lapis lazuli or coloured hard glasses, in which the oxides are not liable to change, should be used, and should be laid on marble or stucco encased in stone, and no animal or vegetable substances, except pure carbonaceous matter, should be used in the pigments, and none should be mixed with the varnishes.