8 Mr. J. J. Waterstou on Capillarity 



Tlie value of Q for turpentine within parentheses was deter- 

 mined by linear integration of the contours of two phases of the 

 drop suspended in tube B, as described in § 2 ; but tlie circum- 

 stances were unfavourable. The capillaiy power of turpentine 

 being small, the ehaugc in the position of the centre of gravity 

 that could be observed before the drop broke ofl' did not exceed 

 ■»^Lth of an inch. The evaporation between the observations must 

 also have affected the result. 



§ 10. A few observations were made with tubes and plates to 

 ascertain the influence of heat in modifying capillary force. 



In a glass retort, water mixed with small flowers was kept at 

 a boiling temperature over an Argand lamp. The stopper being 

 removed, a capillary tube filled with water was suspended by a 

 brass wire within the retort ; also a thermometer with its bulb 

 close to the tube at the level of the top of the capillary column. 

 The lower end of the tube was about half an inch above the sur- 

 face of the water in the retort. The versed sine of the undeve- 

 loped drop on the lower surface of the tube was about one-fifth 

 the external diameter*. 



In this kind of observation the interior of the tube is apt to 

 dry, and the column descends very gradually, much below the 

 true capillary level. By tilting it up and down, it may be kept 

 wet ; and good observations may be made in this way, as the 

 lower drop does not sensibly alter. 



The temperature at the top of the column was kept at about 



95° C, the atmospheric temperature being about 28° C. In a tube 



with round bore ^j^th of an inch diameter, the column diminished 



2 



— for a difference of temperature of G6-5 Centigrade degrees. 



With thermometer-tubes of flat bore the decrement amounted to 



from -pj- to r^r, and with plates r--. These ratios were confirmed 



by another set of observations, made by plunging the tubes into 



* The height of the cohimu in a tube of small bore is but little affected 

 by the size of the th-op at the base. lu a tube of :iVth of an inch internal 

 diameter, and jth of an inch external diameter, the maximum height occiu's 

 when a drop has broken off, the versed sine of the sjiherical segment of 

 water attached to the base being then about Jth the external diameter. Tlie 

 following arc a few of the observed heights and versed sines ; — 



Height of capillary ci'lumn Virscd sine of volume 

 above base of tube. suspended at base. 



in. in. 



1-850 -025 



1-856 -100 



1-838 -125 



1-825 -150 



1-796 -200 (drop about to break) 



1-875 -050 (di-op just broken) 



