106 PETER GUTHRIE TAIT 



GLENLAIR, 



DALBEATTIE, 



Nov. 13, 1867. 

 Dear Tait 



If you have any spare copies of your translation of Helmholtz on 

 " Water Twists " I should be obliged if you could send me one. 



I set the Helmholtz dogma to the Senate House in '66, and got it very nearly 

 done by some men, completely as to the calculation, nearly as to the interpretation. 

 Thomson has set himself to spin the chains of destiny out of a fluid plenum as 

 M. Scott set an eminent person to spin ropes from the sea sand, and I saw you 

 had put your calculus in it too. May you both prosper and disentangle your 

 formulae in proportion as you entangle your worbles. But I fear that the simplest 

 indivisible whirl is either two embracing worbles or a worble embracing itself. 



For a simple closed worble may be easily split and the parts separated 



but two embracing worbles preserve each other's solidarity thus 



though each may split into many, every one of the one set must embrace every one 

 of the other. So does a knotted one. 



yours truly 



J. CLERK MAXWELL. 



Here Maxwell expressed very clearly one of the ideas which Tait finally 

 made the starting point of his discussion of knots. The trefoil knot, the 

 simplest of all knots, was chosen by Balfour Stewart and Tait as a symbolic 

 monogram on the title page of the Unseen Universe ; and some of the 

 speculations put forward in that work must have been closely connected with 

 the line of thought which found a scientific development in Tail's later papers. 

 It may have been while thinking out the attributes of vortex atoms in an 

 almost frictionless fluid that Tait came to see there was a mathematical 

 problem to attack in regard to the forms of knotted vortex rings. 



If we take a cord or, better still, a long piece of rubber tubing, twist it 

 round itself in and out in any kind of arbitrary fashion, then join its ends so 

 as to make a closed loop with a number of interlacings on it, we get a vortex 



