PoiseuiUek Law at Very Loir Rates of* Shear. 685 



Result of observations at various azimuths. 



Azimuths 8. 7. <>. 5. 4. :'>. 2. 1. 



Wave-lengths... -J-OOOT/i ^-Q-0038 +00L13 -00102 -0-O12.3 +00027 -0-0021 -0-0062 



Azimuth mark 1 uYuotes that the telescope of the apparatus 

 was directed X. 29° E., 3, X. 16° W. 3 5, X. CI W., &c. 



These numbers may be confidently pronounced to be due 

 to errors of observation. We computed from them several 

 curves of the theoretical form, having their origins at sixteen 

 equidistant points in the half circumference; this was done 

 by the method of least squares. The most probable of these 

 curves had an amplitude of 0*0073 wave-length, and its zero 

 was half way between the azimuths marked I and 5. Th e 

 average of the given observations is 0*0076 wave-length : 

 after subtracting the ordinates of the computed curve, the 

 mean residual was O'OOb'G wave-length. The sum of the 

 <quare< of the residuals before was 565 . 10~ 4 ; afterwards it 

 was 329 . 10"*. 



We may therefore declare that the experiment shows 

 that if there is any effect of the nature expected, it is less 

 than the hundredth part of the computed value. If pine is 

 affected at all as has been suggested, it is affected to the 

 same amount as is sandstone. If the aether near the appa- 

 ratus did not move with it, the difference in velocity was less 

 than 3*5 kilometres a second, unless the effect on the materials 

 annulled the effect sought. 



Some have thought that the former experiment only proved 

 that the aether in a certain basement-room was carried along 

 with it. We desire to place the apparatus on a hill, covered 

 only with a transparent covering, to see if an effect could be 

 there detected. As the Rumford Committee have allowed us 

 thus to utilize an unexpended balance, we hope to make the 

 experiment in this form, should it be possible to make obser- 

 vations in trying conditions. 



LXITI. Poiseuille's Law at Very Low Rates of Shear. By 

 A. Welmeb Duff, M.A., LJ.Sc. {Edin.), Professor of 

 Physic '.s in Worcester Polytechnic Institute, Worcester, 

 Mo 



POISEUILLB t showed that the law of flow of a viscous 

 liquid through a capillary tube, now usually called 

 Poiseuille's law, holds true through a very wide range of 

 velocity of flow. The rate at which the moving liquid is 



>mmimicated by the Author, 

 t Poiseuille, Compt. Rend. vol. xv, p. 1167 (18^2). 

 Phil. Man. S. 6. Vol. \). Xo. 53. May 1905. 2Z 



