The radiometer, an instrument which revolves continuously under the influence of radiation

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Seite 25 - To the extremity of each arm is fastened a thin disc of pith, white on one side and lamp-blacked on the other, the black surfaces of all the discs facing the same way. The whole is enclosed in a thin glass globe, which is then FIGS.
Seite 18 - Before this instrument can be used as a photometer or light measurer, means must be taken to cut off from it all those rays coming from the candle or gas which are not actually luminous. A reference to the spectrum diagram (Fig. 5) will show that at each end of the coloured rays, there is a large space inactive, as far as the eye is concerned, but active in respect to the production of motion — strongly so at the red end, less strong at the violet end. Before the instrument can be used to measure...
Seite 38 - Here, then (Fig. 9), is an instrument carrying a magnet, and outside is a smaller magnet, delicately balanced in a vertical position, having the south pole at the top and the north pole at the bottom. As the inside magnet comes round, the outside magnet, being delicately suspended on its centre, bows backwards and forwards, and, making contact at the bottom, carries an electric current from a battery to a Morse instrument. A ribbon of paper is drawn through the " Morse " by clockwork, and at each...
Seite 14 - Calling the action of radiation from a candle on the lamp-blacked disc 100, the following are the proportions obtained : — Lamp-blacked pith 100 Iodide of palladium 87*3 Precipitated silver 56 Amorphous phosphorus .... 40 Sulphate of baryta 37 Milk of sulphur 31 Red oxide of iron 28 Scarlet iodide of mercury and copper 22 Lamp-blacked silver 18 White pith 18 Carbonate of lead 13 Rock-salt...
Seite 34 - ... have been exhibited at the Royal Society, where their novelty and unexpected indications excited a considerable amount of interest. This form of instrument is of too recent a construction for me to be able to do more than draw brief attention to a few of the many uses for which it is applicable. By timing the revolutions of the instrument when exposed direct to a source of light — a candle, for instance — the total radiation is measured. If a screen of alum is now interposed, the influence...
Seite 20 - The experimental observations and the numbers which are required by the theoretical diminution of light with the square of the distance, are sufficiently close, as the following figures show : Candle 6 feet off gives a deflection of 218-0° 12 , 54-0° 18 24.
Seite 10 - Now, the part at the red end of the spectrum possesses, in the greatest degree, the property of causing the sensation of warmth, and of dilating the mercury in a thermometer, and of doing other things which are conveniently classed among the effects of heat ; the centre part affects the eye, and is therefore called light ; whilst the part at the other end of the spectrum has the greatest energy in producing chemical action. But it must not be forgotten that any ray of the spectrum, from whatever...
Seite 25 - Exposed to a candle 20 inches off another instrument gave one revolution in 182 seconds ; with the same candle placed at a distance of 10 inches off the result is one revolution in 45 seconds ; and at 5 inches off one revolution was given in n seconds. Thus it is seen that the mechanical action of radiation is inversely proportional to the square of the distance. At the same distance 2 candles give exactly double, and 3 candles give three times, the velocity given by i candle, and so on up to 24...
Seite 26 - ... in a given time is in proportion to the number of candles ; two candles giving twice the rapidity of one candle, and three, three times, &c. The position of the light in the horizontal plane of the instrument is of no consequence, provided the distance is not altered ; thus two candles...
Seite 25 - ... the same way. The whole is enclosed in a thin glass globe, which is then exhausted to the highest attainable point and hermetically sealed. The arms of this instrument rotate with more or less velocity under the action of radiation, the rapidity of revolution being directly proportional to the intensity of the incident rays. Placed in the sun or exposed to the light of burning magnesium, the rapidity is so great that the separate discs are lost in a circle of light.

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