Experiments with the Displacement Interferometer

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Carnegie Institution of Washington, 1915 - Interference (Light) - 113 pages
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Page 36 - ... symmetrical to the vertical axis of the pendulum and submerged in water or some other liquid. In such a case, the mass of the compound pendulum may be reduced in any degree without serious difficulty from capillary forces, as will be shown elsewhere. Since the center of buoyancy is in the vertical axis of the horizontal pendulum, the above equation needs but slight alteration. Let V be the volume of the float, so that Vpg is the buoyancy. Apart from the temperature conditions, p — 1, and hence...
Page 11 - The polar moment of inertia of a surface is the moment of inertia with respect to an axis through the center of gravity...
Page 71 - ... suspended from the horizontal pendulum on opposite sides of a fixed parallel identical plate ; also by charging pairs of plates to a given difference of potential for a given distance apart. So far as can be seen, the repulsion is caused by the condensation of air on the surface of the plates by molecular and not by gravitational force (which is too small). Hence, the method employed should enable the observer to find the density of the concentration in terms of the distance from the plate and...
Page 32 - ... may be slid off to the left, and then the whole remainder lifted off its bearings without touching the pendulum, as the case has no rear wall. The front face is within three inches of the face of the pier. This arrangement was found very satisfactory. The head of the case ki is of course glass faced (identical plates) in front and rear, so that the grating, etc., may be seen. A convex mirror if placed at g reflects a beam of light showing the pendulum to be nearly stationary during the day, in...
Page 30 - Introductory. — The displacement of ellipses or of interference lines in the spectrum is probably capable of being photographed for continuous registry, though less easily than the motion of a spot of light. At all events, it seemed interesting to endeavor to register the excursions of the horizontal pendulum by displacement interferometry, not so much with a view to recording seismological phenomena, as to approach by this means certain other problems, the tilting of the earth's surface relatively...
Page 36 - One may also note that it is smaller, not only as 0 is smaller, but as h/R is smaller. Hence a symmetrical form of pendulum,, like the balance beam, but slightly heavier on one side, suggests itself for work on gravitational attraction, etc. It was not found difficult to reduce the weight of the pendulum by flotation to 40 grams, ie, about 31 times. Hence the force per vanishing interference ring computed above would now be •Barus, this Journal, xxxvii, p.
Page 39 - If long columns of glass are to be inserted in either beam (GJf or GN) the concave mirror is not available, since the direct slit images will then have different focal positions. The rays issue from the plane parallel column, parallel to this focal direction, but from a virtual focus nearer the concave mirrors. Hence, if the column is placed in the beam GM, the beam GN will, as a rule, have to be correspondingly shortened. The algebraic relations are complicated. 5. Observations icilh the interferometer.
Page 33 - ... complementary frame work is shown in fig. 3 and holds the slits of the collimator (or the filament of a Nernst lamp) and the two telescopes T and T' in place for observation, T being used for the direct slit image and T' for the diffraction spectra and interferences.
Page 53 - ... interferometer. 3. Observations. — The brass plates of the preliminary work were soon replaced by a set, larger in area but thinner, this being in the direction of the improvement of method indicated. The same unnecessarily heavy steel pendulum had, however, to be...
Page 41 - For discs 20cm in diameter, however, the result is an invariable repulsion, several times as large as the estimated gravitational attraction, the position of equilibrium being reached gradually in the lapse of several minutes.

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