FIELD DIRECTION SHOWN BY ARROWS To show the direction of an electric field, solid arrows are used. These have an advantage over simple lines because the arrow head gives an indication of the direction in and out of the screen. This is difficult to see from the lines only or indeed from a picture without hidden surface removal. The examples here show the electric potential round molecules. The molecule shown on the left is enalapryl. The arrows indicate a coherent field at the upper centre of the molecule, drawing positively charged objects towards the oxygen atom. The arrows have also been coloured to show the field strength. The molecule on the right is adenylkinase, a protein which is concerned in body metabolism. Here the arrows are not distributed uniformly, but are formed into streamlines. These follow the path of a very small (that is assumed weightless) positively charged particles acting under the influence of the electric field of the protein.