Most modern home brewers are familiar with the hydrometer-a calibrated scientific instrument commonly used to calculate the alcoholic content of beer. While the hydrometer is believed to have been invented in the late 4th century, its calibration for the manufacture of beer did not occur until the late 18th century. John Richardson's book The Philosophical Principles of the Science of Brewing popularized the use of the hydrometer, more accurately known as the "saccharometer," in brewing. Richardson provides valuable insight into important developments in 18th-century brewing technology; technology that has changed relatively little since. This classic reprint of this rare book is a interesting and valuable addition to the resource library of anyone seriously interested in historical brewing or homebrewing.