A. Michelson and E. Morley. On the Relative Motion of the Earth and the Luminiferous Ether. // American Journal of Science - Third series - Vol. XXXIV, No. 203. - Nov. 1887.

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c 9 d

T

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9

ence in white

fringes

but finer; it also had an adjustment in the direction of the incident ray, sliding forward or backward, but keeping very accurately parallel to its former plane.- The three adjustments of this mirror could be made with the wooden cover in position.

The paths being now approximately equal, the two images of the source of light or of some well-defined object placed in front of the condensing lens, were made to coincide, the telescope was now adjusted for distinct vision of the expected interference bands, and sodium light was substituted for white light, when the interference bands appeared. These were now made as clear as possible by adjusting the mirror ef then white light was restored, the screw altering the length of path was very slowly moved (one turn of a screw of one hundred threads to the 5 inch altering the path

nearly 1000 wave-lengths) till the colored interfer-reappeared light These were now given a convenient width and position, and the apparatus was ready for observation.

The observations were conducted as follows : Around the cast-iron trough were sixteen equidistant marks. The apparatus was revolved very slowly (one turn in six minutes) and after a few minutes the cross wire of the micrometer was set on the clearest of the interference fringes at the instant of passing one of the marks. The motion was so slow that this could be done readily and accurately. The reading of the screw-head on the micrometer was noted, and a very slight and gradual impulse was given to keep up the motion of the stone; on passing the second mark, the same process was repeated, and this was continued till the apparatus had completed six revolutions. It was found that by keeping the apparatus in slow uniform motion, the results were much more uniform and consistent than when the stone was brought to rest for every observation ; for the effects of strains could be noted for at least half a minute after the stone came to rest, and during this time efiects of change of temperature came into action.

The following tables give the means of the six readings ; the first, for observations made near noon, the second, those near six oclock in the evening. The readings are divisions of the screw-heads. The width of the fringes varied from 40 to 60 divisions, the mean value being near 50, so that one division

X

means 0*02 wave-length. The rotation in the observations at noon was contrary to, and in the evening observations, with, that of the hands of a watch.

Noon Observations.

16.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16*

July 8.......

44*7

44-0

43*5

39*7

35*2

S4-7

34-3

32*5

28-2

26*2

23*8

23*2

20-3

18-7

17*5

16*8

13T

July 9.......

57-t

57*3

58*2

59*2

58*7

60*2

60-8

62*0

61-5

633

65*8

67*3

69-7

70*7

j. 73*0

70*2

72-2

July 11.....

27-3

23*5

22-0

19*3

19-2

193

18-7

18-8

16-2

14*3

13-3

12*8

13*3

12*3

I 10-2

7-3

6*5

Mean!.......

43*1

41-6

41*2

39*4

37-7

38*1

37-9

37-8

353

34*6

at'3

34*4

34*4

33-9

33*6

31-4

30*8

Mean in w. 1.

862

*832

*824

*788

■754

*762

*758

'756

706

692

*686

*688

688

678

672

628

616

*706

692

*686

688

*688

678

672

*628

:616

Final mean.

784

762

1 '755

738

721

720

715

692

661

P. M. Observations.

July 8.......

61*2

63*3

63'3

68-2

67-7

69-3

70-3

69*8

69*0

713

71*3

70-5

71-2

71-2

70*5

72*5

75'7

July 9.......

26-0

26-0

28-2

29-2

31*5

32-0

313

31-7

33-0

&V8

36-5

37-3

38-8

41-0

42'7

43*7

44-0

July 12......

66*8

66*5

66-0

643

62-2

61-0

613

59-7

58-2

55"7

53-7

54*7

55*0

58-2

58-5

57-0

56*0

Mean.......

51-3

51*9

52*5

53-9

53-8

54*1

54-3

53-7

53*4

54-3

53*b

54-2! 55'0

56-8

572

57*7

58-6

Mean in w. 1.

1-026

r038il*050ir078

1*076

1-082

1-086

1-074

1-068

1-086

1*076

1-084

1*100

1*136

1-144

1-154

1*172

T068

1-086| 1*076! 1-084

1-100

1-136

1-144

1-154

1-172

Final mean.

1*047

1-06211-063! 1-081

1-088

1-109

1-115

1-114

1-120

The results of the observations are expressed graphically in fig. 6. The upper is the curve for the observations at noon, and the lower that for the evening observations. The dotted curves represent one-eighth of the theoretical displacements. It, seems fair to conclude from the figure that if there is any dis-

6.

placement due to the relative motion of the earth and the luminiferous ether, this cannot be much greater than 0*01 of the distance between the fringes.

Considering the motion of the earth in its orbit only, this



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