Lectures on natural philosophy the result of many years' practical experience of the facts elucidated. With an appendix: containing, a great number and variety of astronomical and geographical problems. Also some useful tables, and a comprehensive vocabulary / [Margaret Bryan].

Margaret Bryan

Date:: 1806

Credit: Lectures on natural philosophy the result of many years' practical experience of the facts elucidated. With an appendix: containing, a great number and variety of astronomical and geographical problems. Also some useful tables, and a comprehensive vocabulary / [Margaret Bryan]. Source: Wellcome Collection.

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$It is by the pressure of the atmosphere that \vc raise water from a Avell by means of the common pump; which, like many other familiar operations, is a philosophical experiment. We know' that the pressure of the atmosphere is capable of raising and supporting thirty inches of mercury, Avliich arc equal to the weight of a column of water thirty-four feet high, and no more. Therefore, water cannot be raised by this jjump to a greater height than thirty-four feet; nor is it constructed to raise it so high, because the weight of the atmosphere is sometimes much lessened. The wooden trough, a, fig. 2, pi. 9, represents a well from which water is to be raised, and the cylinder a, fig. 2, the body of the pump: b is the moveable })iston, in which, at c, is a hole covered by a piece of brass, called the valve, which opens upwards only: there is also a valve at the bottom of the barrel, at d, opening in the same direction. Eaperimenf. When I raise the piston, I bring up a column of air out at the top of the pump. The air in the barrel is thus rarefied, by which means the pressure of the external air acts more powerfully on the surface of the water in the well than that from the top of the pipe. By degrees, a perfect vacuum is produced within the-barrel; and the water conseipicntly rises to the top, and then runs out at the spout. 3’his operation would reipiire no labour were it not for the friction of the piston, and the pressure of the external air on the surface of the water above it, Avhich renders it heavy. Experiment. E, fig. 2, ]il. 9, is called a forcing-pump ; it is used for raising water to a considerable height, by the condensation of air. There is no valve to the jiiston, a, of this pump, which, being solid, when drawn uj) reduces the air in the Imrrel, by which means the water rises above L$