During this process, two alternate motions or adjustments must be constantly made; the communication between T and the boiler must be opened, and that between T´ and the boiler closed, which is done by one motion of the regulator. The condensing pipe at the same time must be brought from V to play on V´ which is done by the lever placed upon it. Again the communication between T´ and the boiler is to be opened, and that between T and the boiler closed; this is done by moving back the regulator. The condensing pipe is brought from V´ to V by moving back the other lever, and so on alternately. For the clearness and convenience of description, some slight and otherwise unimportant changes have been made in the position of the parts.[10] A perspective view of this engine is presented in fig. 9. The different parts already described will easily be recognised, being marked with the same letters as in figs. 6, 7. [Footnote 10: In the diagrams used for explaining the principles and operations of machines, I have found it contribute much to the clearness of the description to adopt an arrangement of parts somewhat different from that of the real machine. When once the nature and principles on which the machine acts are well understood, the reader will find no difficulty in transferring every part to its proper place, which is represented in the perspective drawings.] (33.) In order duly to appreciate the value of improvements, it is necessary first to perceive the defects which these improvements are designed to remove. Savery's steam engine, considering how little was known of the value and properties of steam, and how low the general standard of mechanical knowledge was in his day, is certainly highly creditable to his genius. Nevertheless it had very considerable defects, and was finally found to be inefficient for the most important purposes to which he proposed applying it. At the time of this invention, the mines in England had greatly increased in depth, and the process of draining them had become both expensive and difficult; so much so, that it was found in many instances that their produce did not cover the cost of working them. The drainage of these mines was the most important purpose to which Savery proposed to apply his steam engine.