Contact- Angle of Liquids and Solids. 



Ill 



Ether. April 11, 1888. 

 Specific density 0*725. Constant of diameter 1*0 millim. 



<?• 



A-N. 



*. 



I 



a q \ 



a k \ 



T. 



84-0 



3-84S 



3-151 



62-5 



4-875 



4-880 



f 19-2 

 \21-5 



85-55 



3759 



3156 



56-5 



5-043 



4-889 





84-3 



4-002 



3165 



70-5 



4-923 



4-933 





81-65 



3730 



3-120 



575 



4-940 



4-779 





85-15 



3096 



3-102 



55 



4993 



4718 





84-65 



3848 



3151 



62-5 



4950 



4 880 



T19-4 



85-45 



3-768 



3129 



59 



5-035 



4809 



1 21-8 



85-5 



3-705 



3-153 



53 



5-029 



4-875 





84-75 



3-802 



3163 



59 



4-955 



4-911 





85-2 



3-696 



3-138 



53-5 



4-995 



4-827 





85-5 



3-795 



3140 



60 



5039 



4-844 





84-6 



3848 



3161 



62 



4-943 



4-9 LI 



J 19-4 

 122 



! 





Means... 



4-977 



4-855 





Probable errors of means 



{ 



a? 0-010 

 C7, 2 0011. 



Sources of Error. — Before discussing the bearing of these 

 results upon the question of the existence of a finite contact- 

 angle, it is important to consider the possible sources of con- 

 stant error in a set of observations. These mostly affect the 

 measurement of q. If the tank is so placed that the wall 

 through which the observations are made is not vertical, or 

 nearly so, the distance measured by the microscope and the 

 value of q deduced from it will be a little too small. The 

 same result will follow if the microscope is not horizontal in 

 its supports. If the microscope does not move in a horizontal 

 plane, the value of q will be in error. A flaw or a series of 

 striae in the glass wall will also possibly affect a set of obser- 

 vations as a whole ; for the limitations as to the size of the 

 bubbles used and the position of the pointer are such that any 

 one set of observations is made practically through the same 

 parts of the wall of the tank. 



The value of k may be measured at less than its true value 

 if the vertical microscope is not placed over the centre of the 

 lens. It is, however, easy to set it so that the error shall not 

 exceed one hundredth of a millimetre. An error in the esti- 

 mation of the constant of diameter also introduces an error in 

 the determination of k. The estimation would have, however, 

 to be in error by 2*5 millim. in order to explain the smallest 



Phil Man. S. 5. Vol. 26. No. 159. Aug\ 1888. N 



