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thuongmai1641976
2 năm trước
Cho p là tích của 2016 số nguyên tố đầu tiên chứng minh rằng p-1 và p+1 không phải là scp
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The growth of cities, the construction of hundreds of new factories, and the spread of railroads in the United States before 1850 had increased the need for better illumination. But the lighting in American homes had improved very little over that of ancient times. Through the colonial period, homes were lit with tallow candles or with a lamp of the kind used in ancient Rome-a dish of fish oil or other animal or vegetable oil in which a twisted rag served as a wick. Some people used lard, but they had to heat charcoal underneath to keep it soft and burnable. The sperm whale provided superior burning oil, but this was expensive. In 1830 a new substance called "camphene" was patented, and it proved to be an remained expensive, had an unpleasant odor, and also was dangerously explosive. Between 1830 and 1850 it seemed that the only hope for cheaper illumination in the United States was the wider use of gas. In the 1840s American gas manufacturers adopted improved British techniques for producing illuminating gas from coal. But the expense of piping gas to the consumer remained so high that until mid- century gas lighting was feasible only in urban areas, and only for public buildings for the wealthy. In 1854 a Canadian doctor, Abraham Gesner, patented a process for distilling a pitch like mineral found in New Brunswick and Nova Scotia that produced illuminating gas and an oil that he called "kerosene" (from "keros", the Greek word for wax, and "ene" because it resembled camphene). Kerosene, though cheaper than camphene, had an unpleasant odor, and Gesner never made his fortune from it. But Gesner had aroused a new hope for making illuminating oil from a product coming out of North American mines.

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