A potometer measures how factors such as light, temperature, humidity, light intensity and wind will affect the rate of transpiration. The main type of potometer is the 'bubble' potometer shown in Figure Figure 6.
Physicians recommended against the practice because they did not want medicines associated with punishment. A heavy dose of castor oil could be used as a humiliating punishment for adults, especially political dissenters. Colonial officials used it in the British Raj (India) to deal with recalcitrant servants. Belgian military officials prescribed heavy doses of castor oil in Belgian Congo as a punishment for being too sick to work.
In the old days castor oil was mixed with zinc oxide and used for skin problems and to prevent bed sores for those confined to bed. It was excellent. I would be concerned about using it on the delicate facial skin though - castor oil plant is toxic, ricin is the agent extracted from it.