The damping of horizontal waves on a deep fluid has been measured and compared with published theoretical predictions for the following systems: (1) clean water (frequency range: 50 to 920 c/s); (2) solutions of soluble surface-active agents (frequency range 14 to 800 c/s); (3) aqueous solutions on which has been spread a monolayer of an insoluble surfaceactive agent (frequency 150 c/s). The results for clean water agree closely with the appropriate theoretical equations. Data on the damping as a function of frequency and concentration for a soluble surfaceactive agent (sodium lauryl sulphate) show a relaxational effect, due to desorption and adsorption of the film during the passage of each wave. Three other surface-active agents of different chain lengths have been studied to determine the effect of the rate of desorption on the damping at different frequencies. The results are consistent with theory. Soluble and insoluble films possessing different surface compressibilities and shear viscosities have been studied to find how these factors affect the damping at various surface pressures. Results are in excellent accord with the mathematical theory of Dorrestein (1951): the surface compressional modulus is of prime importance in damping capillary waves, and quite low values of this modulus can cause wave damping which considerably exceeds that at a completely immobile surface.

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This paper was written at the suggestion of Mr. Mieth Maeser, in response to numerous inquiries concerning the methods of photoelastic analysis in use at the Massachusetts Institute of Technology. By the use of any of the usual photoelastic methods the difference of the principal stresses and their direction at any point in a suitable loaded specimen are determined, and through a knowledge of Poisson’s ratio their sum is obtained (and a solution made possible) by a measurement of the lateral deformation of the specimen by means of an interferometer strain gage. This instrument, together with its accessories and their use, is illustrated and described in the paper. Examples of the problems solved by the use of the instrument show its accuracy and the consistency of the results obtained by the method.

As part of a critical review of all testing and measuring equipment in the Cotton Laboratory of the Chicopee Manufacturing Corp., two testing devices, the Saco-Lowell Sliver Tester and the Belger Roving Tester, were rebuilt to run at increased speed, and the behavior of a Tensile Tester was investigated. Increasing the speed of the machines required the reduction of inertia, the substitution of springs for dead weights, and other alterations to reduce vibration. The investigation of the Tensile Tester shows that this machine has inherent characteristics which render it unsatisfactory for use on new materials of high elasticity or others with unusual properties.The speeds of both the sliver tester and the roving tester have been increased by a factor of approximately seven.The Cotton Laboratory of the Research Division of the Chicopee Mfg. Corp., at Chicopee Falls, Mass., is equipped with three conventional pieces of apparatus in the form of a Scott Pendulum Type Tensile Tester, a Saco-Lowell Sliver Tester, and a Belger Roving Tester. As part of a general program to re-equip all the laboratories of the Division for true research work rather than for routine mill testing, each of these devices was studied critically to determine its suitability for the work involved, its adaptability to other uses than that for which it was designed, and its general fitness as a physical instrument. The outstanding defect in all the machines was found to be considerable inertia and a tendency toward vibration which severely limited the operating speed. Improving the Sliver TesterThe Saco-Lowell Sliver Tester con-

The behavior of fast-running cords is analyzed, with particular reference to the behavior of ropes of cloth encountered in a textile finishing plant. Theoretical formulas are de duced whereby the behavior at any point may be calculated, and from them practical deductions are drawn for direct use by the engineer.