Page:Popular Science Monthly Volume 6.djvu/395

Rh limestone, thus forming a complete barrier against attack. Inside the wall of masonry are numerous mounds of earth, and within the line of these mounds is a ditch 4 feet deep and 20 feet wide.

A Cheap Substitute for Bells.—Mr. J. A. Judson, C. E., writes us from Dutch Island, near Newport, that for several years past he has used a steel bar in place of a bell, with very satisfactory results. He caused a bar of steel about one inch and a half in diameter to be forged into an equilateral triangle of about three feet on a side, without uniting the two ends, thus forming an instrument similar in all respects except size to the rude musical appliance called the "triangle," used by negro minstrels and sometimes in brass bands. This is suspended from one of its angles by a rope attached to a simple wooden frame, and is struck by hand with an ordinary steel-faced blacksmith's hammer. A cord attached to the triangle and held in the left hand of the ringer prevents its whirling about when struck. If necessary, it may be permanently lashed, without materially interfering with the vibrations, and could then be rung by some stationary mechanical device. "I may have been fortunate," says Mr. Judson, "in finding an especially suitable bar of steel for the purpose, for it is certainly sonorous and powerful, answering all the purposes of an ordinary factory-bell, at merely the cost of so many pounds of steel, and a few hours of skilled labor."

Heat as a Disinfectant.—In the course of some experiments, made with a view to ascertain how far heat may be employed as a means of disinfecting articles of clothing, Dr. Ransom, of Nottingham, found that white wool, cotton, linen, silk and paper, may be heated to 250° Fahr. for three hours without apparent injury, although the wool shows a faint change of color, especially when new. The same may be said of dyed wools and printed cottons, and most dyed silks; but one kind of dyed silk easily turns brown by this heat, and pink silks of some kinds are also faded by it. The same temperature will, if continued for a longer period, slightly change the color of white wool, cotton, silk, paper, and unbleached linen, but will not otherwise injure them. A heat of 295°, continued about three hours, more decidedly singes white wool, and less so unbleached and white cotton and white silk, white paper, and linen both unbleached and white, but does not materially injure their appearance. The same heat, continued for about five hours, singes and injures the appearance of white wool and cotton, unbleached linen, white silk and paper, some colored fabrics of wool, or mixed wool and cotton, or mixed wool and silk. It is noteworthy that the singeing of any fabric depends not alone on the heat used, but also on the time during which it is exposed. In the experiment, the heat was obtained by burning gas with smokeless flame, and conducting the products of combustion, mixed with the heated air, by means of a short horizontal flue, into a cubical chamber through an aperture in its floor, and out of it by a smaller aperture in its roof. Fixed thermometers showed the temperature of the entering and outgoing currents, which represented the maximum and minimum temperatures of the chamber. A self-acting mercurial regulator maintained the temperature of the entering current at any required degree.

The Science of Education.—One of the most important papers read in the Section of Economic Science of the British Association was that by Mrs. Grey on the "Science of Education." The author complained that in Britain there is no adequate or general conception of what education is, and therefore of the magnitude and complexity of the facts on which a science of education, which can never be an exact, but only a mixed and applied science, must be based. We start with a confusion of terms, using education as synonymous with instruction; and the confusion of thought indicated by this misnomer runs through our whole treatment of the subject, theoretical and practical, and is shown in every discussion of the subject. It is surely time that this confusion should be replaced by a scientific conception of the process which should result in the most valuable of all products human beings developed to the full extent of their natural capacity. What is wanted is, that teachers, like practical navigators,