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to us. The sounding balloons have gone up higher and higher until they burst, and then the apparatus carried by them falls down to the ground. You might think it would get hopelessly smashed by such a fall (from a height of 20 miles, say), but the burst balloon case acts as a kind of parachute, or drag, so that the blow on the ground is not really so very hard, and also the apparatus is attached to an ingenious light framework called a "spider," which eases the blow still further: so that usually it is not damaged, and not only does it tell us what happened to it in the upper layers, where man has never reached, but it can be used again and again to get more news. The news has been of intense interest to scientific men, but would scarcely interest us enough to justify dwelling longer on it. Rather, let us return to the bottom layer and recall a few things which have happened in it.

Let us begin with the mountains. Many people have ascended mountains and got above the clouds. In order to get above the clouds they have put a magnificent observatory on Mt. Wilson in California, 6000 feet above the dust, which can also be seen lying below them. Astronomers have begun to use mountains not only to get above dust and clouds, but because they also get above a considerable amount of air. Professor Campbell went up Mount Whitney, sometimes called the "top of the United States," to make observations upon Mars, especially to see whether it has an atmosphere containing water vapour. He made his arduous expedition in order that he might not mistake for water vapour in Mars what really belonged to our own Earth. Having