in Free Surf aces of Liquids. 139 



As we see, the oscillation-period (the determination of which, 

 as the mean of only four oscillations, was not very exact) 

 is constant in each individual series — i. e. independent of the 

 magnitude of the amplitude. It increases, when series A, B, 

 C are compared, with the projection of the upper edge out of 

 the free surface. There can be no doubt that this is to be 

 ascribed to the action of attraction- forces in consequence of 

 the curvature of the surface. The decrements slowly lessen 

 when the amplitudes become smaller; and this diminution is 

 pretty uniform in all the series. I have therefore not attempted 

 to search out its more precise law, but have contented myself 

 with taking, in all the further experiments I have to commu- 

 nicate, a mean value of the logarithmic decrement in each case 

 from ten oscillations, in which the initial and final amplitudes 

 lay in the interval from 400 to 100 scale-divisions. The great 

 difference in the absolute values of the decrement between 

 series A on the one hand and series B and C on the other, is 

 to be attributed to the influence of the free surface. 



I have above referred to the necessity of inclosing the liquid 

 to be studied in a narrow vessel with parallel sides. The proof 

 of this is given by the experiments communicated in Table II. 

 Here also distilled water was experimented with, and the same 

 brass plate as before employed. Under A in this, as in all the 

 following tables, the distance of the upper edge of the plate 

 from the free surface of the liquid is to be understood. If the 

 edge lay below the same, and therefore within the interior of 

 the liquid, the positive sign is employed ; if it projected above, 

 the negative. 



The distance between the displaceable glass plates is indi- 

 cated by the quantity e ; e= co signifies a vessel of such dimen- 

 sions that any influence of the side walls was inconceivable. 

 The oscillation-period T is given here also, in order to show 



the influence of the attracting forces. Lastly, the quantity ^ 



(which was always multiplied by 1,000,000 to avoid decimal- 

 places) serves as the measure of the frictional resistances. 



The values of the oscillation-period are in the first two 

 series nearly constant; in the third series the attraction of the 

 side- walls makes itself perceptible; and this influence comes 

 out still more strongly in the last series. 



