138 



Note. These, together with the simplified (iauss and Codazzi equations, should 

 give by integration the required surfaces. In the attempt to perform the integration, the 

 following geometric solution was readied. I hope to complete the solution by integration 

 later. 



The r-curri-K make principal sictionn. 



The equation of principal normal to the surface is 



dx dx 



— = - along v-curve 



ds dsv 



dx 



=: — , since dSv ^ i/E du = du 

 du 



const. 



X y z 



which is the normal to the surface at (x, y, z). 



