Ben Nevis Observatory.—Interior.
lights and mirrors, and (3) a temperature and moisture indicator. The rain gauge in the garden is a receptacle provided with a funnel through which the water runs, and the depth to which the earth would be covered if it were flat and there were no means of escape for the water, is recorded by a lever, which moves a pencil, the pointed end of which touches a piece of cardboard. Even lightning is made to record itself. A little stream of water for ever running through a pipe projecting from the wall of the observatory picks up any electricity in the air, and carries it into an instrument, which automatically notifies its presence.
Outside the dome, Kew.—The anemometer.
Photography enters largely into the work of the Observatory. By its means it is possible to secure records more reliable and more complete than those of the human hand and eye could ever be. In taking a picture of the clouds, to determine their height and rate of motion, one operator stands on the roof of the Observatory and another is placed half a mile away across the park. The two positions are connected by the telephone, and both men expose their plates at the same instant, so that the cloud is caught from the two points simultaneously. Photography has also, as Professor Huggins in his fascinating address before the British Association in August last showed, been of incalculable service in enabling the astronomer to learn more and more of the marvels of the heavens. Innumerable stars which are invisible to the eye of man through however powerful a glass, are caught by the sensitive dry plate, and, as will be seen from our picture of the sky at night (for which we are indebted to the Editor of Knowledge), their number is very great. The large, diamond-like star is one of those which are visible to man's naked orb. At Kew, however, astronomical photography has been limited to investigations of the
