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Page 384 - Shallow pits are dug, which are partially filled with straw, and on the straw flat pans containing water are exposed to the clear firmament. The water is a powerful radiant, and sends off its heat copiously into space. The heat thus lost cannot be supplied from the earth — this source being cut off by the non-conducting straw. Before sunrise a cake of ice is formed in each vessel.
Page xxxvii - I measure), has been taken as being the ten-millionth part of the quadrant of a meridian passing through Paris ; that is to say, the ten-millionth part of the distance between the equator and the pole, measured through Paris. It is equal to 39-3707898 inches. The metre is divided into one thousand millimetres, one hundred centimetres, and ten...
Page 498 - ... circumference, one of which contains a notch and the -other a serrated knife with a spring-pressed bar running along each, side of it. The machinery is so adjusted that the knife catches the paper exactly between each sheet, and, the paper being held hard on each side by the spring bar, cuts it in two all but a couple of tags near each end, which are left for the purpose of pulling the sheet on between two sets of running tapes, until it is caught by a pair of small rollers which are driven at...
Page xxxix - Ib. raised to a height of one foot in one minute of time. The force competent to produce a velocity of one metre in one second, in a mass of one gramme, is sometimes .adopted as a unit of force. • Unit of Heat.
Page xxxix - In this country the unit of mechanical work is usually the foot-pound, viz. the force necessary to raise one pound weight one foot above the earth in opposition to the force of gravity. A horse-power is equal to 33,000 Ib.
Page 543 - ... sufficient protection for an ordinary building against any thunder-storm in this climate. The copper wire may be built into the wall to prevent theft, but it should be connected to any outside metal, such as lead or zinc on the roof, and to metal rain-water pipes. In the case of a powder-mill, it might be advisable to make the network closer by carrying one or two additional wires over the roof and down the walls to the wire at the foundation. If there are water- or gas-pipes which enter the...
Page xxxvi - Treasury, a new standard yard, bearing the proportion to a pendulum, vibrating seconds of mean time, in the latitude of London, in a vacuum, and at the level of the sea, as 36 inches to 39
Page xxxvi - ... simplest decimal system of multiplication and division, we are enabled to perform with speed and ease any calculations connected with it which may be necessary; another is that the same prefixes are used for measures of length, surface, capacity, and weight ; and, finally, these various measures are related to each other in the simplest manner. Unit of Length. — The English unit of length is the yard, the length of which has been determined by means of a pendulum, vibrating seconds in the latitude...
Page 543 - ... but if there are no such metallic connections with distant points, it is not necessary to take any pains to facilitate the escape of the electricity into the earth. Still less is it advisable to erect a tall conductor with a sharp point in order to relieve the thunderclonds of their charge.