. The principles of physics. wo tin plates, in the latter of which a slit iscut. Allow a beam of calcium light to pass through the slit in S, andthence through the converging lens L and the prism P, and form a spec-trum on a screen, H. Hold in the flame of a Bunsen burner, B, a pellet REVERSED OR DARK LINE SPECTRUM. 379 of sodium; it bums vividly, and the lidit has to pass through the in-tensely yellow flame. We should naturally expect that the yellow of thespectrum would now be more intensely illuminated, but, instead, a darkband in the yellow now appears. It is not really black, but compara-
. The principles of physics. wo tin plates, in the latter of which a slit iscut. Allow a beam of calcium light to pass through the slit in S, andthence through the converging lens L and the prism P, and form a spec-trum on a screen, H. Hold in the flame of a Bunsen burner, B, a pellet REVERSED OR DARK LINE SPECTRUM. 379 of sodium; it bums vividly, and the lidit has to pass through the in-tensely yellow flame. We should naturally expect that the yellow of thespectrum would now be more intensely illuminated, but, instead, a darkband in the yellow now appears. It is not really black, but compara-tively dark. Next hold the plate T between the burner and the condensers so thatthe calcium light may be cut off from the upper portion of the slit,leaving the light from the sodium flame alone to pass through this partof the slit. The spectrum R formed by this part consists of a brightyellow line on a dark ground, being the radiation spectrum of sodium.(It should be borne in mind that the image of the slit is inverted.) The. Fig. 287. other half. A, shows a dark line on the continuous spectrum. We thushave, contiguous to each other, the bright line spectrum of sodium andits reversed, dark line, or absorption spectrum. If you use salts of lithium,potassium, strontium, etc., in a similar manner, you will find in everycase your spectrum crossed by dark lines where you would expect to findbright lines. « It thus appears that the vapors of different substances absorbor quench the very same rays that they are capahle of emittingwhen made self-luminous; very much, it would seem, as agiven tuning-fork selects from various sounds only those of 380 ETHER DYNAMICS. a definite wave-length corresponding to its own vibration-period. 1 The dark places of the spectrum receive light infull force from the salted flame; but the light is so feeble,in comparison with those places illuminated by the calciumlight, that the former appear dark by contrast. Light- trans-mitted through certain liquids
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
