Page:Popular Science Monthly Volume 52.djvu/149

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tirely different kinds; and the woodpecker and warbler in the tree tops select still others. The practical value of birds in controlling insect pests should be more generally recognized. It may be an easy matter to exterminate the birds in an orchard or grain field, but it is an extremely difficult one to control the insect pests. It is certain, too, that the value of our native sparrows as weed destroyers is not appreciated. Weed seed forms an important item of the winter food of many of these birds, and it is impossible to estimate the immense numbers of noxious weeds which are thus annually destroyed. If birds are protected and encouraged to nest about the farm and garden, they will do their share in destroying noxious insects and weeds; and a few hours spent in putting up boxes for bluebirds, martins, and wrens will prove a good investment.

Kites and Balloons in Meteorology.—The recent development of the kite for meteorological purposes, Mr. A. Lawrence Roche says in his paper on the subject, has taken place in the United States, while the use of automatic balloons for obtaining data at very great altitudes has hitherto been confined to Europe. Kites appear to have been first applied in meteorology by Alexander Wilson in Glasgow, who in 1749 raised thermometers attached to them into the clouds. Next was Franklin's electrical experiment. Between 1883 and 1885 E. D. Archibald made differential measurements of wind velocity by anemometers raised on kites fifteen hundred feet. In 1885 A. McAdie repeated Franklin's experiment on Blue Hill; and he afterward made other electrical experiments with kites. The invention of lightweight self-recording instruments made it possible to obtain graphic records in the air by means of kites; and the introduction of tailless kites by Mr. Eddy added to their usefulness. The thermograph raised by S. P. Ferguson, of Blue Hill, in August, 1894, was no doubt the first instrument recording continuously and graphically to be raised by kites; and it permitted simultaneous observations to be obtained in the free air and near the ground. This method of studying the meteorological conditions of the free air has ever since been in regular use at the Blue Hill Observatory. Probably the greatest elevation yet attained by kites, and certainly the highest level to which kites have lifted a meteorograph, is 8,740 feet above Blue Hill. This was accomplished October 8, 1896, by the aid of nine kites, having a total area of 170 square feet, which gave a maximum pull at the ground of about a hundred pounds. The meteorograph remained during several hours higher than a mile, and good records of the indications of the barometer, thermometer, and hygrometer were brought down. More than one hundred records of atmospheric pressure, temperature, and relative humidity of the air, or wind velocity at intermediate heights up to the extreme altitude mentioned have been obtained. Kites furnish a ready and accurate method of measuring the heights of certain low and uniform clouds. Changes of wind direction in the different air strata are determined from the azimuths of the kites. To reach much higher altitudes than three miles unmanned free balloons have been considerably used in France and Germany. These balloons, which carry self-recording apparatus, rise until equilibrium is attained in the rarefied air, when they lose their buoyancy and fall to the earth. Most of them have been recovered, with the instruments and records uninjured.

The Education of an Engineer.—Criticising the present methods of education, especially for qualifying students in mechanical science, Mr. G. F. Deacon asked, in his British Association sectional address, "Are we not in some cases attempting, at too early a stage, the teaching of subjects instead of principles? I mean including the practical working of details which will become the regular work of the student in the office or works of an engineer. . . . I do not say that subject training of this kind at college may not be useful; but we have to consider whether it does not, for the sake of some little anticipation of his office work, divert the attention of the student from the better mastery of those principles which it is so essential for him to grasp at the earliest possible time, and which do not limit his choice in the battle of life to any branch whatever of the profession or business of an engineer, but which, on the contrary, qualify him better to pursue with success whatever branches his inclination or his opportunities