We get here, then, the essential features of that steam engine which is so familiar to all who travel by land or by sea. But these early atmospheric engines were not invented for the purpose of transport: it was for the pumping of water from mines that they were principally contrived, and in the case of the Newcomen engine, the other end of the beam opposite to that which was worked upwards by steam pressure (and downwards by atmospheric pressure) was attached to pump-rods that worked in connection with the buckets for pumping out the water. Thus, like the movement of the see-saw, when the piston-rod was down at the bottom of the cylinder the pump-rods were correspondingly elevated, and vice versa. As soon as the piston descended to the base of the cylinder through the cessation of the vacuum the spray of cold water was stopped, and steam was again admitted into the cylinder to cause another upward stroke. At the same time it was necessary to discharge the hot water which had accumulated at the bottom of the cylinder, and this was done through a pipe fitted with a valve which would not allow of its return; any air admitted with the steam and the cooling water was blown out through a snifting valve (so-called because of the noise it makes) as the powerful steam came in. But, the reader may ask, what about the open top of the cylinder? How can it be any good to use an uncovered cylinder in conjunction with steam? The answer is, that since the top of the piston was always kept flooded with water, all air was excluded. We have thus seen the steam engine in its most elementary form; how that it employs boiling water until it becomes steam which is then admitted to a cylinder and by its own force moves a tight-fitting disc or piston up and down. We have also seen that by attaching a rod to this disc, and, further, by connecting this rod to a beam, we can make the latter go up (by means of the steam pressure) or come down (through the pressure of the air). In order to effect the latter we have remarked the fact that a vacuum had to be made by condensing the steam through spraying cold water.