The early history of the English air-pump has been latterly allowed to fall into great confusion, so that the steps by which the instrument was improved, the periods at which those improvements were made, and the parties by whom they were effected, are all more or less confounded with each other, or mis-stated.

It is in connection with the double-barrelled air-pump, that the accepted history of the instrument is chiefly erroneous, but the mistakes made in reference to the more complex engine, have ultimately involved in confusion even the authentic records of the steps by which the earlier single-barrelled air-pump was improved, so that the account of its successive alterations must commence with its earliest and simplest construction.