On the table are various other pieces of equipment that the natural philosopher would have used during his demonstration: a thermometer, candle snuffer and cork, and close to the man seated to the right is a pair of Magdeburg hemispheres, which would have been used with the air pump to demonstrate the difference in pressure exerted by the air and a vacuum: when the air was pumped out from between the two hemispheres they were impossible to pull apart. The air pump itself is rendered in exquisite detail, a faithful record of the designs in use at the time. What may be a human skull in the large liquid-filled glass bowl would not have been a normal piece of equipment; William Schupbach suggests that it and the candle, which is presumably lighting the bowl from behind, form a "vanitas"—the two symbols of mortality reflecting the cockatiel's struggle for life.