Science Siftings

New Zealand Tablet, Volume XXXV, Issue 12, 21 March 1907, Page 35

Science Sif tings

By •Volt*

The British Museum. . According to some interesting - statistics of the library of the British Museum, the number of books which it contains is 1,750,000, not counting single sheets or parts of "works that axe accumulating. The shelving of the library exceeds 69 miles in length. Why Leaves Turn Brown. The green matter in the "tissues of a leaf is com- .- posed of two colors,_ red and blue. When the sap ceases to flow in the autumn the natural growth of the tree is retarded, . and oxidation of the tissues takes place. Under certain conditions , the green of the leaf changes to red^. Under different aspects it takes a yellow or brownT" hue. The difference in color is due to the difference in combinations of the original constituents of the green tissues ,and to the . varying conditions of climate, exposure arid soil. Maples, and oaks have the brightest color. Oceans Below Us. - " 'So enormous is the quantity of the water contained below the surface of the earth that if it should be poured out upon the. land- it would cover it to a „ depth of about 4000 feet,' is the remarkable assertion of a geologist. ' Below a depth of about six miles it is believed that no water, can exist in the rocks, because the tremendous pressure probably closes all pores, but above that level the amount of underground water is estimated to be equal in quantity to one-third of all the water contained in all the oceans.' : • No Sunset for Five Days. At the head of the G-ulf of Bothnia there is a mountain on the summit of which the sun v shines perpetually during the five days of June 19, 20, 21, 22, and 23. Every six hours during this season of continual sunshine a steamer leaves Stockholm crowded with visitors anxious to witness the phenomenon. At tiie same place during winter the sun disappears and is not seen for weeks. Then it comes in sight again for 10, 15 or 20 minutes, gradually lengthening its stay , until finally it stays in sight continually for upward _ of 120 hours. The Height of a Mountain. The barometer is the instrument by . which the . - weight of *the atmosphere is determined. But how many of you know that- this instrument may also be used to determine the height of a mountain ? It .has been found, that the column of mercury -in the barometer falls about one inch to every increase of 1000 feet mi altitude, because the higher we ascend the lighter is the atmosphere and the less, therefore, • the pressure on the mercury in the reservoir of the instrument. If the barometer marks thirty »inohes, then,* at sea level and twenty-seven inches on top -of a •mountain, it follows that the mountain is 3000 feet in height approximately. How we Got Thermometers. It is believed tthat Galileo - made , the first thermometer about the year 1595. *It was an instrument of glass, consisting of a bulb from which the slender tube depended, open at its lower end, and there plunged into a vase containing some colored liquid, such. as vinegar or wine. The glass bulb was heated before the stemi was immersed, and when the contained ais cooled and contracted the fluid in the upright thermoscopic tube rose to a higher leveL This simple and primitive apparatus is constantly made use of on the lecture table* nowadays, when some simple demonstration of the laws of heat is to be made. Acetylene Gas. Acetylene gas is now used as^ an explosive. By means of an air mixture a foroe is obtained from it which; cam compete., with that of powder and dynamite. Carbide of calcium is reduced to small particles and put into a tin box. -In this the carbide lies at the bottom and above it is a portion filled with water. After the drill hole has been completed the cartridge is placed in it, and the hole is closed with a wooden stopper. Then the partition is perforated -by a blow fromi a pin and the water comes in, contact with the carbide,- whereby acetylene gas; is generated.- This mixes with the air 'of the drill hole. After five minutes the gas is ignited by an electric spark.