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Page:Popular Science Monthly Volume 18.djvu/150

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THE POPULAR SCIENCE MONTHLY.

The Westinghouse Automatic Brake.—The well-known Westinghouse air-brake, invented and so largely used in this country, seems to be rapidly gaining in favor abroad. The English journal "Iron," in a recent issue, highly commends it as answering all the requirements of a perfect brake, as laid down by the Board of Trade, and gives some valuable statistics concerning its use. From returns received up to the 20th of last July, it appears that the number of applications of the automatic brake throughout the world is—to engines, 3,277, and to carriages, 13,502. This is an increase in less than fourteen months of 1,594 to engines, and 6,255 to carriages. Besides this, there are 2,472 engines and 8,812 carriages fitted with the nonautomatic brake—that is, the one using ordinary air-pressure. This, then, makes a total of 5,749 engines and 22,314 carriages fitted with this apparatus. In the case of 678 engines and 2,720 cars a change has been made from the non-automatic to the automatic. This equipment is divided between the different countries as follows: The United States has 2,211 engines and 7,224 cars using it; England 456 engines and 2,942 carriages; in France there are but 203 engines and 1,609 carriages; and in Belgium 197 of the former and 1,241 of the latter. The number in use in Germany, Russia, and Holland is small, ranging from 55 to 28 engines and 93 to 117 carriage equipments. A few are also in use in Italy, Sweden, and the British provinces. Certain very excellent improvements and additions "Iron" points out have recently been made to this brake system, which greatly increase its usefulness. There are a method of lighting the cars and a means of communication with the engineer by the passengers. The light is produced by carburetting air in a manner somewhat similar to that in common use in the numerous portable gas-machines. The air is reduced from the high pressure necessary to operate the brakes to a moderate and steady one. It is then passed into a small iron box containing sponges saturated with gasolene, and from these passes to the burners. The light is said to be of good quality and sufficiently bright to see to read fine print in any part of the car. Its cost is much less than gas or any other material commonly used for this purpose on railroads. The communicating apparatus consists of an arrangement of air connections, such that the pulling of a handle in the car starts a whistle on the engine and on the car, and puts the brakes partially on. The attention of the engineer being attracted, he can complete the application of the brakes if he is in a favorable position for stopping, or, if not, release them. The handle once pulled, the passenger can not return it to its place. This can only be done by one of the trainmen, so that improper use of the apparatus is readily detected. This appliance is especially designed to meet the requirements of passengers in the compartment carriages, such as are used abroad. With the American system of cars, the bell-rope furnishes a ready means of communication, while the trainmen are generally within easy call. The lighting and communicating apparatus can be added to carriages after the brake is put in, and but one connection between the carriages is required.

 

The Circulation of Sap in Trees.—Professor Joseph Böhm has suggested, as a theory to account for the circulation of the sap in plants, that the exhaustion of the water by evaporation from the top of the plant causes a difference in pressure in the adjoining cells, which produces a sucking up of the fluid from the cells that are relatively rich to those that are relatively poor in water. He has also endeavored to make clear what is the purpose of those vessels which run the whole length of deciduous trees, and which can be easily perceived with the naked eye in sections of many species, as the oaks, maples, etc. Generally these vessels have been regarded as air-vessels, but Professor Böhm has been convinced that in many plants they not only receive sap by measured transpiration, but also in consequence of an active exhalation take up a relatively great quantity of water, so that the air fails to penetrate them at the ordinary pressure and only escapes in considerable quantities after the plant has become drier. It has also been shown that the branches of many plants, willows for instance, notwithstanding their vessels are supplied with fluid, are able to take up more water from without, and in such quantities that twigs will increase in weight twenty