The Elements of Surface Tension (Abstract)

Many of our ordinary statements about surface tension are true only when properly qualified. Common laboratory experiments give correct values only when correction terms are used. A number of surface tension paradoxes will be given

Electricity and Mechanics

When electric charges are in motion the forces between them differ from the electrostatic forces. The magnetic concept is used to take account of these non-electrostatic forces. The magnetic effect of a moving charge is relative to the electrostatic extremely small except when the velocity approaches that of light. However due to the circumstance that the electrostatic effects often, as in a wire carrying a current, practically cancel, the magnetic forces are very important. According to our present beliefs any field of force changes in an analogous manner if it be moved. There is theoretically the same excuse for speaking of a magnetic field about a moving mass as a moving charge. The difference is that in this latter case the discrepancy from the gravitostatic force is not of practical importance

A Method Obtaining Absolute Values for X-Ray Energy Levels

X-ray absorption edges usually correspond to the removal of the orbital electron to some definite outer level, not to complete ionization. The difference between this state and the state of complete removal from the metal is not known. It is probably of the order of 25 volts. By measuring the energies of photoelectrons produced by known photons the energy levels can be definitely placed. The experiment suggested is a modification of the one recently described by Kretschman (Phys. Rev. Vol. 43, p. 417)

Mean Free Paths of Molecules and the Wave Mechanics

Direct experimental determination of the mean free paths of hydrogen, nitrogen and oxygen have led to a value of the effective cross section of the molecule between 4 and 5 times greater than that obtained from viscosity measurements. Massey and Mohr have shown that assuming the rigid sphere molecule the wave mechanics leads to a difference in the values; the theoretical ratio, however, is not greater than 2

Ubi Facit Ibi Est

Where a thing acts there it is. In place of the old dogma of Descartes, Cogito ergo sum, the modern pragmatist says that a thing exists if it affects us; we have an objective rather than subjective philosophy

Fundamental Dimensions and Electrical Units

Proposition: What dimensions and how many are fundamental is a matter of choice, custom and convenience, not of logical necessity. Limitation: This does not deal with how many and what fundamental entities are required to build a universe; it is simply a question of mensuration; how many and what independent dimensions shall (must) we use to express physical quantities unambiguously, and to make physical equations balance

Mean Free Paths of Gases

A molecular beam passes through a chamber enclosing gas at low pressure. The emergent beam is measured on a Pirani gauge. The question has been raised whether a collision in the classical sense has any meaning without specification of the angle of scattering considered. As a preliminary experiment it was determined that the molecules suffering very small deviations (less than a degree) were negligible in number. The mean free path of H2, He, N2, O2, molecules have been measured; in each case the values found are smaller (by several fold) than the values determined indirectly from kinetic theory. The difference is probably due to neglect of the persistence of velocity in the kinetic theory

An Opportunistic Laboratory

A laboratory has a joint function (a) to create happy attitudes and (b) to teach subject matter practically and realistically. It has sometimes been questioned whether the laboratory does act effectively either as inspiration or as a teaching device. The paper describes experiences in a laboratory where the experiments were exactly correlated with the class work, where laboratory manual was dispensed with, where the experiments were usually unconventional

Mean Free Paths of Gas Molecules in Mercury Vapor

The mean free paths have been obtained for hydrogen, helium, nitrogen, carbon dioxide, methane, ethane, propane, butane and isobutane through mercury vapor. The decrease in intensity is observed as a beam of the gas passes through the vapor, any deviation as great as a half degree removing the molecules from the beam. The free paths measured in this way are, as is expected, several times smaller than the values determined from viscosity data

Mean Free Path of Gases by a Direct Method

Apparatus consists of a brass tube partitioned into chambers. Partitions contain small holes which are exactly aligned. Gas is introduced at a pressure of several millimeters at one end; a vacuum is maintained in other chambers by rapid pumping and the molecular beam passing through the aligned holes is measured by impact upon a vane suspended from a quartz fiber. Introduction of a gas in one of intermediate chambers deflects away a definite proportion of the beam giving a direct measure of the mean free path