Step 11 With the new shape selected, choose the Pen tool (P) and hover over the bottom anchor points until a minus sign is displayed next to the cursor. Click twice to delete the anchor points. This leaves a gentle curve, so use the Convert Anchor Point tool (Shift + C) and click on the bottom two points to convert them into corners.
Step 12 With the Direct Selection tool (A), select the bottom two points of the new shape by clicking and dragging a box over just them. Now click on one of them and drag them downwards to make the bell jar shape a little taller, holding down Shift to keep them in a straight line.
Step 13 Select the Ellipse tool (L). Click and drag an ellipse to form the bottom of the belljar. Using the ellipse of the extruded isometric circle as a guide, resize it to fit at the bottom of the bell jar shape.