Rybcznski Theorem:

Now, we consider the effect of charges in endowment (of labor or capital) on the output. For  this we need  to consider only the equations (xxiv) and  (xxv). We have already noted the coefficients are functions of factor prices only, i.e.,

Thus,  if either L or K  changes, aij's  remain constant. Under  this assumption, differenting (xxiv) and (xxv) i.e., with respect to L, we have,  

These results  are  known  as  the  Rybcznski  theorem. They are  perfectly intuitive. It can,  for example, be said  that an  increase in endowment of labor (holding output prices constant) will  increase the output of the labor-intensive industry and  decrease the output of the capital-intensive industry. Analogous explanation follows for an  increase  in the endowment of capital.
Now, we offer a diagrammatic illustration for the proof of Rybcznski theorem.  Here, assumption is that  there  is multiple production technique  such  that the  contract  curve  is  smooth  and  always lies below  the diagonal.

Since the wage-rental  ratio is unchanged, optimum factor will be unchanged. The new  production  point  is E₁. O₂' E₁ and O₂ E_o are parallel to each other. Clearly, there  is an  increase in  the production of good yl  (of  the sector -1) and fall  in  production of y₂  (good of the sector -2),  since 0₂' E_l = 0₂  G <  0₂ Eo. lncrease in  the endowment of labor causes expansion of labor intensive good (here X₁). Since endowment of capital is fixed  it is to be released from the sector-2, which  involve contraction  of y. Therefore, production of  increases more than the actual increase in  the endowment of labor. This is known as the 'magnification effect'.