Page:Popular Science Monthly Volume 53.djvu/65

Rh kites over a pulley, which turns so as to deliver it 111 any direction to them. There is also a wheel which records the pull of the line, and a provision for recording the measurement of length. Thus the relation of wind pressure to pull, and several other matters, can at any minute be figured out.

The purpose of the observatory from the first was to secure by means of kites a more elevated plane of observation than could be obtained by other means. As soon as the corps had acquired skill in kite making and flying, a self-registering thermometer was sent up; afterward they were able also to add a barometer, these being carried on a base, covered by a wire basket, and attached to the line as high among the kites as it could be sustained.

But the two instruments did not furnish a record of all the elements; and finally a complete "meteorograph" was devised. Externally, this was a cage of wire one foot in height, the same in width, and half that in the other dimension. The weight of a similar one used in Washington is two pounds and a half. The combination within consists of a thermometer, barometer, hygrometer, and anemometer—all making record on a sheet of paper wound on a cylinder that is revolved by clockwork. As the direction of the wind is ascertained by the drift of the kites, each flight furnishes the observers with five meteorological elements. No doubt they will be able ere long to determine the electrical conditions at different heights with equal accuracy.

Every well-constructed kite has a fixed capacity for ascending to a certain height—not more than a few hundred feet usually, because of the increase in the weight of the line and the wind's pressure on it; therefore, in order to reach a greater altitude, it became necessary to connect another kite to aid in the lifting. Still higher flights required a further addition of kites, until sometimes a dozen, ranging in size from five to twelve feet, were up in the same tandem, requiring a small rope to hold them. A large and divided wind surface was necessary, else in lulls the kites would descend and the instruments with them; so the obtaining of observations was at great cost of time, labor, and money. In a fresh wind the vigorous efforts of three strong men were required for two or three hours to bring a large tandem down. Several times, in strong winds, the kites have broken away, only reaching the ground two, four, and nearly six miles distant; yet nearly every time they have been recovered without having sustained much damage.

For the reason mentioned on a previous page, some two years since, No. 14 steel music wire (the size of small piano strings) was substituted for the line of vegetable fiber. A mile of this wire weighs from twelve to fifteen pounds, which is much lighter than