340 Mr. C. Barus on the Change of the Order of Absolute 



of the thread of marine glue. The effect of the cylinder of 

 viscous fluid in the reservoir a may be neglected from its 

 large radius. 



ha. By way of digression I may add another similar case ; 

 viz. that of a viscous liquid like glycerine, transpiring in a 

 vertical capillary tube, in virtue of the weight of its own 

 column only. In this case P=(L + £)£#, 8 being the density 

 of the liquid, g the acceleration of gravity, L the initial head 

 of the column. Inserting these quantities and integrating, 

 equation (2) becomes 



v 



v= 



8(WLln£±!) 



An example of results obtained in this way is given in the 

 following Table. The observations, though made upon a 

 single descending thread at the end of each half minute, are 

 grouped in two batches., The tube was dry • perhaps a moist 

 tube (adhering thin film of glycerine) would have been 

 preferable. 



Example. — Viscosity of Glycerine. 

 r=-0505 centim. ; L=1'35 centim. ; 8=1-26 ; A*=120 sec. 



t 



I. 



V> 



t. 



I 



n- 



sec. 



cm. 



ff/es. 



sec. 



cm. 



g/cs. 



SO 

 150 



1007 

 20-30 



] 5-05 



270 

 390 



29-82 

 38-60 



\ 5-53 



60 

 180 



1272 



22-75 



j 5-07 



300 

 420 



31-95 

 40-83 



j 5-46 



90 

 210 



15-30 

 25-10 



| 5-11 



330 

 450 



34-20 

 43-04 



) 5-44 



120 

 240 



17-80 

 27-43 



j 5-13 



360 

 480 



36-40 

 45-22 



j 5-43 



To account for the difference of rj in the two sets of results 

 is beyond the present purpose. It is noteworthy * that each 

 measurement of rj occupies but two minutes, even admitting 

 that the tube is unfavourably wide ; for in the case of viscous 

 liquids the temperature-effect is of great importance, and this 

 expeditious method therefore has some advantages. The 

 experiment may be varied by observing the descending upper 



* Cf. Graham, Phil. Trans, cli. p. 382 (1861) :— " The liquid (glycerine) 

 is too viscous to be transpired by means of the bulb and capillary em- 

 ployed in these experiments." I am not aware that the viscosity has 

 been measured since. 



