Summary. The device for splitting a plankton sample into two approximately equal parts consists of a hollow cylindrical drum mounted to turn on a horizontal axis, and a vertical semi-circular septum cemented into place midway between the end walls of the drum. About a quart wilt fill the drum up to the axis. After rotating the drum until the septum is above, the sample is poured in. Then the drum is rotated until the septum splits the sample. Lifting the drum ahd rotating a little more, the two separated samples are drained into containers of convenient shape for emptying and filling. Smaller samples are obtained by emptying one container into the drum. Thus aliquot portions o F approximately 1/2 , 5/4, 1/s , etc. of the original are obtained, and the process is continued until the sample is small enough for counting. In general the sample consists of a number of different kinds of plankters each of which is counted separately. Multiplying each count in the ruth fraction by 2m gives an estimate of the number in the original sample. Each step in the splitting process is subject to random errors and possibly biased errors. Studies of these errors are based upon a series of test runs involving both volume measurements and plankton counts. The samples split were specially chosen to represent different types of plankton communities.The several types tested proved not to influence the results materially.Statistical tests involving distribution of Z 2 and departure from the mean, of left and right portions gave convincing evidence that the errors .were random.Thus, averaging separate counts would be expected to reduce the error. Researches on the magnitude of the error were based upon the law of propagation of errors of a product. Furthermore a study of the difference between the left and right samples as well as other investigations on the different sources of error have been made.
Interrelations between processes of radiation, convection, and evaporation near the sea surface are determined quantitatively, for the North P acific Ocean. The object was to investigate these processes of heat changes as a whole rather than to consider any one of them in detail. In particul ar, revised values of a coeffi cient giving the time rate of temperature change were determined for use in a method of calculating surface currents from temperature. Observations of a twenty-year series of North P acific Ocean surface t emperatures in an eastern area extending from latitude 20° to 50° were selected so as to be least influenced by ocean currents. Monthly averages for 5° quadrangles prepared and published by the Imperial Japanese Observatory at Kobe were used as a basis for calculatin g these normal temperatures corresponding to half degree latitude intervals. Values of the average daily solar radiation reaching the sea surface, during each month, prepared and pub1ished by H. H. Kimball of the U.S. Weather Bureau and measurements of the amount of solar radiation at variou depths provided the additional observational material used. Equating the time rate of change of the amount of heat in an elementary volume of water to that furnished by the absorption of penetrating solar radiation less the rate of loss led to a simple differential equation whose solution expressed the theoretical sea temperature in t erms of time, latitude and depth for depths less than 35 meters. The amount of solar radiation at each of a series of depths was assumed to be reduced in a constant ratio for each of the equ al depth intervals, and the rate of loss of heat was ass umed to vary in proportion to the temperature. These theoretical temperatures agreed closely with the observed ones. The coefficient in the expression for the rate of loss of heat was calcul ated first from its relation to the lag (one to three months) between maximum t emperatures a nd m aximum radiation, and minimum temperatures and
BY GEORGE F. MCEWEN. 'HP V HE purpose of the following investigation was to devise a method '-*• by which Stokes's law of the frictional resistance of a fluid to the motion of a sphere whose center performs small periodic oscillations could be applied to the measurement of the coefficient of viscosity of fluids. The two main objects were: first, to obtain as close an agreement as possible between the actual working conditions and those demanded by theory; second, to devise a process of measuring the force acting on the sphere, even for fluids having a very large coefficient of viscosity. The contents of this paper fall under the following five heads; I. The effect of the internal friction of fluids on the motion of pendulums, from Sir G. G. Stokes's Math, and Phys. Papers, Cambridge, 1880 and 1901, Vols. I. and III. II. An account of the method adopted in the present investigation to overcome the difficulties mentioned by Stokes, and to more nearly realize in the experimental work the ideal condition assumed in the theory from which Stokes's law was deduced. III. Experimental tests of the present method. IV. Suggestions for future research. V. Summary of the paper. I. THE EFFECT OF THE INTERNAL FRICTION OF FLUIDS ON THE MOTION OF PENDULUMS. I. Observations on the Motion of Pendulums, An account of the experiments made by Bessel, Baily, Dubuat, and Sabine, and the theoretical results obtained by Poisson, Challis and Plana is given in Stokes's Math, and Phys. Papers, Vol. III., pp. 1-7. The effect of the surrounding fluid on the time of vibration of a pendulum was computed by Poisson, Challis, Green, and Plana from the hydrodynamical theory of a frictionless fluid. A fair agreement with the observations was found in some cases, but in many cases, especially No. 6.] MEASUREMENTS OF FRICTIONAL FORCE. 493 MEASUREMENTS OF FRICTIONAL FORCE.
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