or dividing by 20x12 to obtain the means in terms of the distance between the fringes,
|
N. |
N.E. |
E. |
S.E. |
S. |
S.W. |
W. |
N.W. |
|
-•002 |
-•Oil |
+ ’003 |
-001 |
-•004 |
-•003 |
-•001 |
+ •018 |
|
N. |
-•002 |
E. |
+ •003 |
N.E. |
-•011 |
N.W. |
+ •018 |
|
S. |
-•004 |
W. |
-•001 |
S.W. |
-•003 |
S.E. |
-•001 |
|
Mean = |
: --003 |
+ *001 |
Mean= |
-•007 |
+ •008 | ||
|
+ •001 |
+ •008 | ||||||
|
Excess |
= -•004 |
Excess= |
= -015 |
The small displacements — 0'004 and -0’015 are simply errors of experiment.
The results obtained are, however, more strikingly shown by constructing the actual curve together with the curve that should have been found if the theory had been correct. This is.shown in fig. 4.
The dotted curve is drawn on the supposition that the displacement to be expected is one*tenth of the distance between the fringes, but if this displacement were only T^, the broken line would still coincide more nearly with the straight line than with the curve.
The interpretation of these results is that there is no displacement of the interference bands. The result of the hypothesis of a stationary ether is thus shown to be incorrect, and the necessary conclusion follows that the hypothesis is erroneous.
This conclusion directly contradicts the explanation of the phenomenon of aberration which has been hitherto generally accepted, and which presupposes that the earth moves through the.ether, the latter remaining at rest.
|
N. |
N.E. |
E. |
S.E. |
S. |
S.W. |
W. |
N.AV. |
|
0-131 |
0-131 |
0-108 |
0-102 |
0*096 |
0*086 |
0*075 |
0-046 |
If x is the number of the column counting from the right and y the corresponding footing, then the method of least squares gives as the equation of the straight line which passes nearest the points x) y—
y = 9‘25x + 64*5
If, now, we construct a curve with ordinates equal to the difference of the values of y found from the equation, and the actual value of y, it will represent the displacements observed, freed from the error in question.
These ordinates are:
It may not be out of place to add an extract from an article published in the Philosophical Magazine by Stokes in 1846.
“All these results would follow immediately from the theory of aberration which I proposed in the July number of this magazine: nor have I been able to obtain any result admitting of being compared with experiment, which would be different according to which theory we adopted. This affords a curious instance of two totally different theories running parallel to each other in the explanation of phenomena. I do not suppose that many would be disposed to maintain FresneFs theory, when it is shown that it may be dispensed with, inasmuch as we would not be disposed to believe, without good evidence, that the ether moved quite freely through the solid mass of the earth. Still it would have been satisfactory, if it had been possible to have put the two theories to the test of some decisive experiment.”
In conclusion, I take this opportunity to thank Mr. A. Graham Bell, who has provided the means for carrying out this work, and. Professor Yogel, the Director of the Astrophysi-calisches Observatorium, for his courtesy in placing the resources of his laboratory at my disposal.
Art. XXII.—Observations on the Light of Telescopes used as Night-Glasses ; by Edward S. Holden.
In the Philosophical Transactions for 1800, vol. xc, p. 67, Sir William Herschel says: “In the year 1776, when I had erected a telescope of 20 feet focal length, of the Newtonian construction, one of its effects by trial was that when toward evening, on account of darkness, the natural eye could not penetrate far into space, the telescope possessed that power sufficiently to show, by the dial of a distant church steeple, what o’clock it was, notwithstanding the naked eye could no longer see the steeple itself. Here I only speak of the penetrating power, for though it might require magnifying power to see the figures on the dial, it could require none to see the steeple.”
I had long been desirous of trying this experiment with a large aperture, and made several attempts in 1874 to have the Dome of the 26 inch Clark refractor at Washington so arranged that a terrestrial object could be seen, but without success. I therefore took the first opportunity to try the effect of a telescope under these conditions at the Washburn Observatory, where the large equatorial commands the horizon. The most suitable object for examination was the tower of the Hospital
