The idea that Earth is a magnet is far from new. It was first proposed in 1600 by a British physician named William Gilbert. Knowing it acts like a magnet is one thing. Knowing why it acts like a magnet is more difficult. In fact, finding out why is a fairly recent discovery. To find out why required new technology. It was the seismograph that made it possible to learn why the Earth acted like a magnet. Seismograph are used to study earthquakes. By studying earthquake waves they were able to learn about Earths interior. They discovered that Earth has an inner and outer core. The outer core consists of liquid metals, mainly iron and nickel. Scientists think that Earths magnetic field is generated here. It is caused by the motion of this liquid metal. The liquid metal moves as Earth spins on its axis.

What did William Gilbert first speculate in 1600?

You may be wondering, how can a glacier get so big? Why does it move? These are both good questions. In the winter months, precipitation falls as snow. This solid form of water builds up on the ground as long as the temperatures stay cold enough. As the temperature rises, the snow starts to melt. The frozen water changes state back into a liquid state. Nearer the poles, summer does not last very long. If the summer is long enough and warm enough, all the snow may melt. This is what typically happens now. The earth was a little cooler 12,000 years ago. As a result, during the summer months, that amount of snow did not melt. It may have only been an inch or so of snow that melted. The following winter, snow fell on top of this left-over snow. This next winters snowfall had a head start. Year after year, the snow that did not melt became thicker and thicker. Inch by inch the snow started to build up. Over many years, layer upon layer of snow compacted and turned to ice.

Why didn't most snow melt in the past?

Elettra stuck the little slip of paper, on which the recipe was written, into her shabby pocket-book without looking at it. She could read and write fairly well, and had been used to helping her husband the under-steward with his accounts at Muro, but even if she had looked at the recipe she would have understood nothing of the doctor's hieroglyphics and abbreviated Latin words. The prescription was for a preparation of arsenic, which Matilde had formerly taken for some time. The chemist would not make any difficulty about preparing twenty doses of it for the Countess Macomer, though the whole quantity of arsenic contained in so many would probably be sufficient to kill one not accustomed to the medicine, if taken all at once. But though Matilde was so anxious to have the stuff before luncheon, she had a number of doses of it put away in a drawer, which she took out and counted, after Elettra had gone. She opened one of the little folded papers and looked at the fine white powder it contained, took a little on the end of her finger and tasted it. Then, from the same drawer, she took a package done up in coarser paper, and opened it likewise, looked at it, smelt it, and touched it with the tip of her tongue very cautiously indeed. It was white, too, but coarser than the medicine. She was very careful in tasting it, and she immediately rinsed her mouth with water, before she tied up the package again, shut the drawer, and put the key into her pocket.
What is the first substance Matilde tastes?