330 
C. GODFREY ON THE APPLICATION OF FOURIER’S 
Rontgen Rays and Ordinary Light: Page 
§ 31. Professor J. J. Thomson’s theory of Magnetic Pulses. Lord Rayleigh’s 
suggestion that these pulses will be equivalent to simple waves of short 
length. 343 
§ 32. The energy distribution to which the Thomson pulses are equivalent . . 343 
§§ 33—35. Energy chiefly in the ultra-violet, but perhaps one-thousandth of it 
in the visible spectrum. Other considerations.344 
§ 36. Sir George Stokes’s theory. Absence of Diffraction. 344 
Radiation of an Incandescent Gas ; Width of Spectrum Lines : 
§ 37. Plane Waves. No absorption taken into account.345 
§38. Doppler effect. Mutual action of molecules-during encounter.345 
§§ 39-40. Finite length of train of waves emitted by a molecule between two 
collisions. This cause will affect the width of the spectrum line when the 
radiation of the gas is analysed. 345 
§ 41. Fourier analysis of a train of m sine-waves.346 
§ 42. Summation for all the molecules of the gas. Expression for the total 
radiation.347 
§ 43. Michelson’s Experiments on the Visibility of Interference Fringes. 
Visibility function for present case. 349 
§ 44. Limiting case of zero pressure.350 
§ 45. Practical evaluation of integrals.351 
§§ 46-48. Comparison of present results with the widths observed by Michelson. 
Observed widths in all cases greater than calculated widths. Comparison 
of present results wdth the results deduced from Doppler’s principle by 
Lord Rayleigh. Spectrum line now found to be similar in structure, 
but 10 per cent, narrower.352 
§§ 49-53. Justification of preceding result.*.354 
Effect of Damping on Widths of Spectrum Lines : 
§§ 54-55. Lommel’s Theory.355 
§ 56. Fourier analysis of damped sine-wave.355 
§§ 57-58. Estimate of magnitude of damping effect.356 
Character of Ether-motion in nearly homogeneous Light: 
§59. Interference fringes wdth white light j Avith nearly homogeneous light . . 357 
§ 60. Nearly homogeneous light may be regarded as a simple vibration Avith 
slowly-varying amplitude and phase. Connection of this rate of A T ariation 
Avith the Avidth of the spectrum line.357 
§ 61. Interference phenomena looked at from the tAvo points of view.358 
§ 62. Interference as limited by the lengths of the free paths of the molecules in 
the incandescent gas.358 
Effect of Natural Light on a Vibrator: 
§ 63. Equation of motion of the vibrator. Effect of light on vibrator depends on 
the spectrum of the light and on the constants of the vibrator.359 
§ 64. Sellmeier’s treatment of the effect of the irregularities in nearly homo¬ 
geneous light. His erroneous conclusion that the natural vibrations of the 
molecules aauII not be aroused. ... 359 
