| Description | Professor Poynting has sent on Ewart's letter to him, but Larmor cannot get a clear idea of what Ewart means. Poynting is not responsible for the conclusion that resistance when air bubbles are present is of capillary origin. Destruction of regularity in flow is a potent cause in itself. He takes the example of Ewart's column and the forces operating upon it, illustrating this with a small sketch. He discusses the distribution of force along the column, diffusion and osmosis. The driving energy that makes sap rise 'is doubtless due to (artificial) evaporation', he believes, and the agency of solar radiation. Larmor is not a botanist and therefore does not know the regulating agencies that control the opposing forces, but he does not think there is any mystery in the character of the physical actions in such control. Larmor continues the discussion and concludes by saying that he is skeptical of Ewart's idea that high pressureis required to drive water through a branch. larmor asks for the letter's return, if Ewart should reply. |