Page:Popular Science Monthly Volume 28.djvu/583

Rh likely to synchronize in their motion. If such parts of a building must of necessity be joined, let them be so joined that the connecting link will force them to vibrate as a whole, and yet resist fracture, Brick chimneys in contact with the framing of a wooden roof are apt to be shorn off at the point where they pass through the roof. Light archways connecting heavy piers will be cracked at the crown. To obviate destruction from these causes a system of building may be adopted which essentially consists of tying the building together at each floor with iron and steel tie-rods, crossing each other from back to front and from side to side. The center of inertia of a building, and of its parts, should be kept as low as possible. Heavy tops to chimneys, heavy copings, and balustrades on walls and towers, heavy roofs and the like, are all of serious danger to the portion of the structure by which they are supported. When the lower part of a building is moved, the upper part, by its inertia, tends to remain behind, and serious fractures often result.

Poteline.—The plastic substance, poteline, introduced by M. Potel, is formed of a mixture of gelatine, glycerine, and tannin, to which may be added sulphate of baryta or zinc-white; and the whole may be colored, if desired, with vegetable colors. Poteline is molded while still hot; and, when it has become cool, yields itself to every kind of manipulation. It can be turned, filed, bored, or screwed, and it is susceptible of a very fine polish, which may be conveyed by pressure. This facility of working permits it to be treated in the same way as bronze, and makes it adaptable for all kinds of mountings. It can also be used to seal bottles and jars hermetically, for the fabrication of dolls' heads that can not be broken, and for the composition of an artificial marble out of which ink-stands, doorknobs, and a thousand other articles can be made cheaply. The proportion of the different materials entering into the composition of this substance varies according to the use that is to be made of it. For sealing bottles, it should be used in a nearly liquid condition; for the manufacture of fancy articles, in an opaque form; while the exact composition of the marble-poteline is a secret known only to the inventor. M. Potel has described a method by which he uses poteline as an envelope, to stop and prevent fermentation and insure the preservation of fruits and meats.

Oyster-Culture in Connecticut.—According to the last report of the Shell-fish Commissioners of the State of Connecticut, the policy of farming out the oyster-grounds to individual proprietor-cultivators has been very successful. The number of persons engaged in the business increased ten per cent during the seven months covered by the report; and the rapid development of the oyster industry is further shown in the continued extension of the area of grounds devoted to it, and in the increase in the number of oyster-steamers. It has been found that with reasonable care and labor the number of star-fish may be so reduced that those enemies shall be incapable of doing serious damage to the oyster-beds. A new enemy, however, threatens the beds, in the shape of a sand-tube-building worm, whose structures cause accumulations that suffocate the oysters; but the estimates are contradictory as to the amount of the damage it is likely to do. Efforts have been made during the past year, with much success, to redeem muddy grounds and make them available for oyster-cultivation by covering them with shells and pebbles brought from the Housatonic River. The demand, both for oysters and for seed-oysters, is constantly increasing, and it is not likely that the supply will soon go ahead of it.

What is a Real Forest?—In all forest culture, says Mr. M. C. Read, in a paper on "The Preservation of Forests on the Head-Waters of Streams," which is published by the Department of Agriculture in "Special Report No. 6," "it should be remembered that, for climatic purposes, an orchard of trees is not a forest. The planting of trees along the highways, about our homes, in parks and proves, ought to be encouraged for a variety of reasons, but will have little of the climatic effect of true forests. A dense growth of underbrush, herbaceous plants, and mosses under the larger trees, which will retain the fallen leaves in place, fill the surface-soil with rootlets, checking