Isometrics relative to Viscosity. 91 



Table I gives an example of my earlier results. The trans- 

 piration tubes were smooth internally as shown in figure 1. 



The table is one of double entry, and the data contained 

 show the absolute viscosity {yj) of marine glue at the stated 

 temperatures and pressures, in terms of one billion g/cs units. 

 The pressure excess is the difference of pressures at the two 

 ends of the tube. 



TOOOatm. 1500atm. 2000 atm. 



>30 000 12-0 >60 000 



8-30 12-0 15-2 



1-12 2-2 



Table I. — 



Mean Values of 77/10' 



Ap = Pressure Excess 



100 atm. 



300 atm. 



Temperature = 8 5° 



" = 18-3° 



= 22-5° 



" = 30-5° 



(2-5) 



•065 



•073 



Rates at 



18-3° 



22-5° 



10~ 9 X ArijAp = 



•0137 

 •0091 



•00220 

 •020 



In constructing the rate of change of viscosity with pres- 

 sure, I assumed that the whole thread transpired at the mean 

 of the pressures at the two ends of the steel tube y or since the 

 pressure at the open end is zero, at half the pressure excess. 

 Furthermore, that 



v P = Vo(i+i>p) = v,(i+tf>4p) 



If therefore A37 be the increment of viscosity corresponding 

 to the pressure iAp, the final data of Table I (rates) are at 

 once intelligible. 



What is chiefly striking in this table is the preponderating 

 influence of temperature. Thus the material, which between 

 20° and 30° C. transpires readily enough, is at 8° so nearly 

 solid, that a burden of 2000 atmospheres, brought to bear at 

 one end of a transpiration tube 10 Gra long and as wide as l cm , 

 is unable to produce perceptible flow even after 5 hours. It 

 also appears that in proportion as the viscosity of a body in- 

 creases with fall of temperature^ its isothermal rate of increase 

 with pressure also increases. 



Some time after, I repeated this work with great care and 

 obtained — 



Temperature = 



1-8° 



•20° 



•22° 



•24° 



'/ 10 9 



2-7 ) 

 5-2 J 



4-3 



•94 ) 

 1-16 \ 



•28 



&xio 3 = 



8-0 ) 

 3-0 X 



1-3 



3'9 ) 



1-8 \ 



4-8 



It would be premature to speculate on the nature of the 

 relation of viscosity to pressure and to temperature, on the 

 basis of these results. As to the pressure coefficient b, one 



