In the 19th century, geologists could tell whether one rock layer was older or younger than another by the fossils they contained. But they could not measure the absolute ages of rocks until after the discovery of radioactivity in the 1890s. Radioactive substances, which are occasionally found in rocks, give off high-energy rays and decay (break down) at a fixed …

Sunset occurs when the upper edge of the sun — called the upper limb — sinks just under the horizon; sunrise occurs when the upper limb rises just above the horizon.

Stem cells, which hold the promise of new cell-based therapies to treat critical medical conditions, have to be effectively stored until it’s time to use them. The method is called cryopreservation: it freezes stem cells at temperatures below -150 o C, by immersing them in nitrogen vapour. But if the cells are to survive this process, they need to be …

Points or index refers to a figure indicative of the health of the stock market. The most widely used index is sensex or sensitive index which is based on weighted value of 30 numbers of most traded shares in the Mumbai stock exchange. Each stock has a percentage share in a total of 100 and affects the value of the …

International Telecommunication Union (ITU) recommendation defines the international public telecommunication numbering plan used in the PSTN. It also defines the format of phone numbers. As per these recommendations, numbers can have a maximum of 15 digits and are usually written with a + prefix. CCITT, the predecessor of the ITU Telecommunication Standardization Sector, developed the first formal list of telephone …

Electric pylons are tall supports – made of galvanised steel lattice, steel tube or wood – used for power line construction. In normal terrain, they are assembled on the site. In mountainous regions, helicopters are used for power line construction, which are efficient but expensive. In the aerial construction method, the entire structure is pre-assembled and shifted in helicopters.

It was not before sixteenth century, an Italian doctor named Jerome Cardan got the idea of teaching deaf-mutes through written characters. As a result of his work finger alphabets were developed, similar to the finger alphabets used today. With the help of finger alphabets, a deaf-mute makes the letters with his fingers and spells out words. He also depends on …

The lab technician selects a lens blank that has the correct segment (called an add) and a base curve close to the prescribed power. Then to make the power match the prescription exactly, another curve is ground on the back of the lens blank. In most labs, the equipment is designed to grind minus curves, so a strong, plus lens …

Clouds are formed when warm moist air rises into the sky. When it reaches a certain height, the warm air cools down and the water vapour in it condenses into small drops of water, forming clouds. There are several different types of clouds. The ones which are highest are usually made up of ice, and are the thinnest. These are …

Although the 1950s are most often considered the 3-D movie decade, the first feature length 3-D film, “The Power of Love,” was made in 1922. Since that time the use of 3-D technology in theaters and on television has drifted in and out of mainstream popularity. But, whether you’ve used them for the big screen or at home in front …