CAPILLAR Y A TTRA CTION. 33 



Take this length on the compasses, and putting 

 the pencil point at P', place the other point at 

 O' on the line P' N', and with o' as centre, describe 

 a small arc, P' P". Continue the process according 

 to the same rule, and the successive very small 

 arcs so drawn will constitute a curved line, which 

 is the generating line of the surface of revolution 

 enclosing the liquid, according to the conditions 

 of the special case treated. 



This method of solving the capillary equation 

 for surfaces of revolution remained unused for 

 fifteen or twenty years, until in 1874 I placed it 

 in the hands of Mr. John Perry (now Professor 

 of Mechanics at the City and Guilds Institute), 

 who was then attending the Natural Philosophy 

 Laboratory of Glasgow University. He worked 

 out the problem with great perseverance and 

 ability, and the result of his labours was a series 

 of skilfully executed drawings representing a large 

 variety of cases of the capillary surfaces of revolu- 

 tion. These drawings, which are most instructive 

 and valuable, I have not yet been able to prepare 

 for publication, but the most characteristic of 



D 



