Page:Popular Science Monthly Volume 46.djvu/732

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tions investigation of the ray of light that has passed through it by spectroscopic examination and by observations of the twinkling of the stars and of the fluctuations on the margins of the larger celestial bodies when viewed in the telescope. The information obtained in these ways must, however, always be vague, because the total result received by us is the integration of the individual effects at each point of the path, and it is not practicable to separate the sum into its parts; while the knowledge obtained would be otherwise incomplete. Other means of systematic exploration of the free air are by towers, like the Eiffel Tower in Paris, kites, pilot balloons (without aëronauts), and balloons carrying aëronauts. Towers do not reach to the height it is desired to explore. The method by kites has been studied especially by Mr. William A. Eddy, of Bergen Point, N. J. Mr. Eddy uses tailless kites, placing them in tandem, and recommends that they be flown in groups of three. By such means he has attained heights of between four thousand and five thousand feet, and expects to reach fourteen thousand feet without great difficulty. Three tailless kites will fly when any one of the three will not in mild surface winds. They easily right themselves when reversed, and a tandem series of kites tends to prevent the jerking which might put the instruments out of order. The best possible anemometer is a balloon which is immersed in the air and moves freely with it. While such balloons can be employed only for the study of air currents, by a proper selection of places and dates and the assistance temporarily of theodolites and persons capable of working with them they could be made very useful. They would enable us to study the arrangement of air currents about definite meteorological phenomena, such as centers of high or low pressure. A more instructive but more expensive method is that of pilot balloons carrying automatic registering instruments. Balloons sent up by M. Hermite in 1892 carried means for the automatic record of pressure and temperature, but were disabled from registering the temperature by the cold stiffening the ink. They also carried a device for releasing and dropping cards for tracing the course of the balloon, which did not operate very satisfactorily. Much better service than this would be given by systematic work by a meteorologist who would make the ascension himself. Evidence points to the conclusion that the cloud layer and perhaps the upper cloud service is a region of especial activity in meteorological phenomena, but the facts on which such a conclusion could be verified are of such character that they would probably escape any automatic registry. Prof. Harrington furnishes estimates showing that the cost of operating any of these methods could be brought within reasonable limits.

Telpherage Lines.—The telpherage method of transportation is much better known in Spain, Italy, and the British colonies than in England and the United States. Its history may be hypothetically traced as an evolution from the single-rope bridges of the Himalayas and Thibet—cables made of twisted birch twigs on which the passenger crosses seated in a hoop, which he hitches forward while he holds the rope above with his hands. The next development is to fasten a cord to the hoop by which it is drawn to either side. A similar rough form of transport, except that buckets and wheels were used instead of the hoop, was employed for many years in the lead mines of the Peak of Derbyshire. A great impulse was given to the method by the invention of twisted steel cables, which made the lines stronger and more lasting. More than two thousand miles of telpher line are now in working order in Spain, Italy, South America, India, Cape Colony, China, and Japan. A line at Hong Kong, rising ten hundred and ninety feet in two miles, is used for the transportation of the European workmen at the port up the mountain at night, in order that they may sleep in purer air. It is led straight up the mountain side on high steel trestles, and carries, in little back-to-back cars, three persons on each side. At Table Mountain, Cape Colony, the suspending wire is carried in a single span fourteen hundred and seventy feet to the edge of the cliff, and thence in another span fourteen hundred feet to the top of the mountain. At the Rock of Gibraltar the wire runs, after a first leap of eleven hundred feet, straight to the summit on a series of lofty trestles in an ascent of one foot to every foot and a half. At