Dimensional Analysis. Dimensional Analysis (also called Factor-Label Method or the Unit Factor Method) is a problem-solving method that uses the fact that any number or expression can be multiplied by one without changing its value. It is a useful technique.
In 1887, the first dry cell battery was invented. Unlike previous batteries, it used a paste electrolyte instead of a liquid.
Inventions of incandescent electric light bulb and of dry battery at the end of the 19th century enabled solution for this problem. First dry cell batter was invented in 1896. It was an improved variant of the previous version in that way that its electrolyte was a paste instead of liquid. Because of that, it could work in any position and it would not break or spill that easily. It was a perfect power source for a portable light source. In 1899, English inventor David Misell invented the first flashlight. It had three D batteries placed in a tube that acted as a handle of the device. Batteries powered a small incandescent electric light bulb and a simple contact switch turned light on and off.