458 Messrs. 0. H. Bosanquet and H. Hartley: JS'otes 



readings were taken with each, no two readings being made 

 with the meniscus in the same place. The average deviation 

 from the mean in each series was 4 per cent., but occasion- 

 ally values were obtained differing by as much as 20 per 

 cent, from the mean, due to large irregularities in the film, 

 such as particles of dust. When such sources of error were 

 detected, the reading was discarded. 



The angle of contact was calculated from the mean result 



of each series of experiments by the formulae T cos Q — ^~—- , 



taking the value of the surface tension of water at 14° 0. as 

 73*4 dynes/cm., as this must be independent of the material 

 of the tube provided there is no contamination of the liquid 

 surface. 



The following results were obtained : — 



Diameter of 

 Tube. 



Mean 

 Depression. 



T cos 9. 



9. 



Temp 



0-0939 cm. 



0-934 cm. 



-21-5 



107° 02' 



15° 



0-1233 



0-673 



-20-4 



106° 08' 



14° 



0-2060 



0-440 



-22-3 



107° 41' 



13° 



0-2403 



0-663 



-21-4 

 Mean 



106° 57' 



14° 





106° 57' 



14° 



The angle of contact between water and paraffin was then 

 determined directly by partially immersing a microscope- 

 slide coated with paraffin in water and tilting it until the 

 surface of the water appeared plane where it met the paraffin. 



Clean dry microscope-slides were dipped into molten 

 paraffin-wax, any superfluous wax was drained off, and the 

 slide allowed to cool in a horizontal position. It was then 

 mounted in a clamp which could be rotated about a hori- 

 zontal axis by means of a tangent screw. The clamp also 

 carried a divided circle which could be read to 5'. 



The slide was first levelled by means of a spirit level and 

 then rotated through about 90°, so that it dipped into a 

 rectangular glass cell containing water supported on a stand 

 with a screw motion for raising and lowering it. 



The cell was raised one or two millimetres at a time and 

 the nature of the curvature of the liquid surface near the 

 plate was observed. The slide was then rotated by means of 

 the tangent screw until after raising the cell and tapping 

 the table on which the apparatus stood, the surface appeared 

 plane right up to the paraffin surface. 



It was found convenient to have the edge of the slide 



