A Manual of Physical Measurements

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Press of the New era printing Company, 1918 - Physical measurements - 223 pages
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Page 190 - As a unit of resistance, the international ohm, which is based upon the ohm equal to io9 units of resistance of the CGS system of electro-magnetic units, and is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice, 14.4521 grammes in mass, of a constant cross-sectional area and of the length of 106.3 centimeters.
Page 104 - ... energy. Less than a gramme (1/28 oz.) would give the Hiroshima explosion. This combined principle will be our number two. Closely allied to number two, and indeed derivable from it by the principle of relativity, is the conservation of momentum, which is identical with what schoolboys learn as Newton's Third Law of Motion : Action and Reaction are equal and opposite. The backward momentum (speed times mass) of a gun just after it is fired is equal to the forward momentum of the shot. When a ship...
Page 10 - The most probable value of a measured quantity that can be deduced from a series of observations made with equal care and skill, is that for which the sum of the squares of the residuals is a minimum." . . . "This is the so-called most probable value, and it is the office of the principle of Least Squares, in any case, to point out the way of arriving at it.
Page 76 - Or in different words, the specific gravity of a body is the ratio of its mass to the mass of an equal volume of a standard substance.
Page 77 - The specific gravity of a solid or liquid is the ratio of the mass of the body to the mass of an equal volume of water at some standard temperature. At the present time a temperature of 4 deg.
Page 101 - X io"w g. cm, where / = moment of inertia of the molecule about an axis through its center of mass and perpendicular to the line joining its nuclei.
Page 105 - If two bodies of the same material moving along the same straight line collide, the ratio of the velocity of separation to the velocity of approach is called the coefficient of restitution.
Page 47 - Readings in ten-thousandths of an inch are obtained by the use of a vernier, so named from Pierre Vernier, who invented the device in 1631. As applied to a caliper this consists of ten divisions on the adjustable sleeve, which occupy the same space as nine divisions on the thimble. The difference between the width of...
Page 213 - If the first finger points in the direction of the magnetic field, the second finger points in the direction of the current, then the thumb will point in the direction of the motion of the conductor.
Page 73 - ... eliminated with perfect certainty, is called the Probable Mean Result. Again, the physicist may wish to obtain the exact weight of a body. No balance is exactly poised so that the two arms are precisely equal. But their difference effects the result by a known law of mechanics. This law shows that by weighing the body first in one pan and then in the other, and taking the geometric mean of the two weights, we shall get the exact answer. Such a mean is the Precise Mean Result. The mean commonly...

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