OCR Text |
Show II I POPULAR SCIENCE IS ance at the mouth of the hole, when it cau be dispatcher with a gun, doy; or other method, as preferred. The inventor in-ventor is Lorenz N. Cornell of Nativi-dad, Nativi-dad, Cal. To Sensitize Postal Cards. The popularity of illustrated postal cards makes it desirable to produce them at home by photography, and all that is needed tor this is the sensitising sensitis-ing of the card.- To do this plunge the card into a 1 per cent solution of chloride of sodium (common table salt), and when it is dry brush the Handy Electric Time Switch. For automatically turning off and on at predetermined times one or more electric lights iu a building without the aid of an attendant, a new mechanism has Been designed. There is a dip! on the face of a clock-like arrangement, ar-rangement, and on an extension of the shaft which carries the single hand two dii';s are mounted, with slots cut from tb.-? center of the circumference. These ('isks are held in place by friction fric-tion and can be set to throw t.ie switch at any desired hour by simply turning them with the hand. As the shaft re- part it is desired to sensitize with a brush which has been previously dipped in a 10 per cent solution of nitrate of silver. Still better results are had by adding to the 1 per cent salt solution an equal quantity of phosphate of soda. Alter the printing tne paper is washed only on the part that contains the image; then it is laid in the gold solution, and finally fixed wilh hyposulphite. Then it must be washed and dried. As these operations opera-tions are all done with a brush, they are accomplished rapidly. Doing them in a dim light, of course, gives the best resuns. , Special Scale for Stores. Quick service in a grocery store has come to be demanded, and in furtherance fur-therance of this demand it is customary custom-ary to put up in advance packages of the most-needed commodities. It is for this work that a special scale has been designed. The scale itself may be of any ordinary pattern, with the usual hopper or scoop and the tilting beam. In addition thereto, the inventor in-ventor provides a source of electrical energy, and a secondary hopper, mounted above the scale hopper, and capable of cutting off the feed the instant in-stant the proper amount of the commodity com-modity falls into the scoop. Suppose the grocer desires to put up pound packages of coffee. He places the counterpoise weight on the pound notch of the beam, tilting the latter down and disconnecting the two contact con-tact points which close the electrical ciruit. The coffee is placed in the hopper above the scoop and immedi- Turns the light off and on automatically. automati-cally. volves it carries the disks with it, and when the slot in the first disk reaches a vertical position below the shaft it allows a pin which has been traveling on the circumference to rise to the center, with the result that a pivoted lever on which the pin is mounted tilts and drops a weight to pull the switch open. When the second disk ' has reached the same position a second sec-ond weight drops with a reverse effect. ef-fect. The Largest Bridges. The Brooklyn suspension bridge 1,595 feet long is still the largest suspension bridge in the world. The new East river bridge has a span of 1,600 feeet, and its capacity is far ; - greater than that of the Brooklyn . - Yiridge. Each of its four cables has J .. " a safe strength of over 10,000,000 pounds in tension. The Washington bridge over the Harlem river consists of two spans of 510 feet in the clear. The Roebling suspension bridge at Niagara was replaced in 1897 by a spandrel-braced, two-hinged, steel arch of 550 feet span. It accommodates accommo-dates the railway tracks on the upper deck and a highway below. The second sec-ond Niagara bridge replaced the Clifton Clif-ton suspension bridge in 3 898, and as . its span is &40 feet it is the largest arch of any type in the world. In 1901 the Pennsylvania rai!road built a "Stone bridge consisting of . - ' - ' - |