128 



Mr. A. Ferguson on the Shape of the 



Now Thomson finds that both carbon monoxide and carbon 

 dioxide contain C+ + , 0+ + , C-f , + , C0 2 + , and C0 + , 

 whereas carbon monoxide alone contains C — . 



Further, Thomson shows that such negatively charged 

 atoms ought to be, and are, less numerous wheu the discharge 

 has difficulty in passing, i. e. at low pressures. 



The spectrum given by carbon oxide at low pressures is 

 also generally seen in vacuum-tubes enclosing hydrocarbons ; 

 but there is evidence that oxygen must be present. Whether 

 this spectrum is to be attributed to C0+ or C0 2 + there is, 

 at present, nothing to show, so far as I am aware. 



XV. On the Shape of the Capillary Surface inside a Tube of 

 Small Radius, with other Allied Problems. By Allan 

 Ferguson, B.Sc> (Lond.), Assistant-Lecturer in Physics in 

 the University College of North Wales, Bangor*. 



§ 1. rpHE present paper is devoted to the formation of a 

 JL closer approximation than usual to the outline of 

 the surface of a liquid contained in a vertical tube of small 

 bore, and to the application of the 

 formula developed to certain cases 

 of practical interest. 



With axes as shown in fig. 1, 

 and symbols having the significance 

 there indicated, the differential equa- 

 tion to the surface of the liquid will x' 

 be 



Fig. 1. 



gp(y+ h ) 



HRi + lJ' 



where Rx and R 2 are the principal 



radii of curvature at the point P. " 



Substituting their values and putting 

 a 2 5%, this becomes 



a 2 x^+a 2 p(l+p 2 )=x{y + h){l+p 2 )l 



Putting p= tan$ ? and s= sin<£, we readily find 



■*"■* 



dz z 

 dx~^~ x~ 



a 2 



(i.) 



* Communicated by Prof. E. Taylor Jones. 



