Page:Popular Science Monthly Volume 13.djvu/575

 a point of surface of the wood is uncovered, be it ever so small, the teredo, still microscopic, penetrates into the interior. Covering wood with sheets of copper or zinc, or with nails, is a too expensive process, and only protects the wood so long as they form an unbroken surface.

2. Impregnation with inorganic, soluble salts, generally considered poisonous to fish and animals, does not protect wood from the attacks of the teredo. This want of efficacy must be attributed in part to the fact that the salts absorbed by the wood are extracted by the dissolving action of sea-water, and in part, also, because those salts do not appear to have a poisonous effect upon the teredo.

3. Although we do not know with any certainty if, among exotic woods, there may not be found those which will resist the teredo, we can affirm that hardness is not an obstacle which prevents that mollusk from perforating his galleries; the ravages observed in the wood of guaiacum and mamberklak prove this.

4. The only means which can be regarded with great certainty as a true preservative against the injury to which wood is exposed from the teredo, is the oil of creosote; nevertheless, in employing this means, care is necessary that the oil be of good quality, that the impregnation be thorough, and that such woods be used as will absorb oil readily.

The conclusions arrived at by our commission are confirmed by the experience of a large number of engineers in the Netherlands, and also in England, France, and Belgium. M. Crepin, a celebrated Belgian engineer, expresses himself thus, in a report on experiments tried at Ostend, under date of February 5, 1864:

M. Forestier, a French engineer at Napoléon-Vendée, in a report dated March 3, 1864, makes a résumé of experiments conducted by himself in the port of Sables-d'Olonne, in the following words:

Under date of Haarlem, April 20, 1878, Prof. Von Baumhauer writes to Edward R. Andrews, of Boston: