Kelvin wrote in 1852, "...within a finite period of time past the earth must have been, and within a finite period of time to come the earth must again be, unfit for the habitation of man as at present constituted, unless operations have been, or are to be performed, which are impossible under the laws to which the known operations going on are subject." In the 1860s, Kelvin employed a mathematical model by von Helmholtz suggesting that the energy of the Sun is released via gravitational collapse to calculate the age of the Sun to be between 50 and 500 million years. He reached comparable figures for the Earth. The missing ingredient here was radioactivity, which was not known to science till the end of the nineteenth century. Electricity, magnetism, and electrification After the Dane Hans Christian Ørsted demonstrated that it was possible to deflect a magnetic needle by closing or opening an electric circuit nearby, a deluge of papers attempting explain the phenomenon was published. Michael Faraday set himself to the task of clarifying the nature of electricity and magnetism by experiments. In doing so, he devised what could be described as the first electric motor (though it does not resemble a modern one), a transformer (now used to step up the voltage and step down the current or vice versa), and a dynamo (which contains the basics of all electric turbine generators). The practical value of Faraday's research on electricity and magnetism was nothing short of revolutionary. A dynamo converts mechanical energy into an electrical current whilst a motor does the reverse. The world's first power plants entered service in 1883, and by the following year, people realized the possibility of using electricity to power a variety of household appliances. Inventors and engineers soon raced to develop such items, starting with affordable and durable incandescent light bulbs, perhaps the most important of the early applications of electricity. As the foremost expert on electricity and magnetism at the time, Lord Kelvin oversaw the laying of the trans-Atlantic telegraphic cable, which became successful in 1866. Drawing on the work of his predecessors, especially the experimental research of Michael Faraday, the analogy with heat flow by Lord Kelvin, and the mathematical analysis of George Green, James Clerk Maxwell synthesized all that was known about electricity and magnetism into a single mathematical framework, Maxwell's equations. Maxwell used his equations to predict the