Joseph Priestley in the context of "Timeline"

A burning glass or burning lens is a large convex lens that can concentrate the Sun's rays onto a small area, heating up the area and thus resulting in ignition of the exposed surface. Burning mirrors achieve a similar effect by using reflecting surfaces to focus the light. They were used in 18th-century chemical studies for burning materials in closed glass vessels where the products of combustion could be trapped for analysis. The burning glass was a useful contrivance in the days before electrical ignition was easily achieved.

The phlogiston theory, a superseded scientific theory, postulated the existence of a fire-like element dubbed phlogiston (/flɒˈdʒɪstən, floʊ-, -ɒn/) contained within combustible bodies and released during combustion. The name comes from the Ancient Greek φλογιστόν phlogistón (burning up), from φλόξ phlóx (flame). The idea of a phlogistic substance was first proposed in 1669 by Johann Joachim Becher and later put together more formally in 1697 by Georg Ernst Stahl. Phlogiston theory attempted to explain chemical processes such as combustion and rusting, now collectively known as oxidation. The theory was challenged by the concomitant mass increase and was abandoned before the end of the 18th century following experiments by Antoine Lavoisier in the 1770s and by other scientists. Phlogiston theory led to experiments that ultimately resulted in the identification (c. 1771), and naming (1777), of oxygen by Joseph Priestley and Antoine Lavoisier, respectively.

In 1769, 18th-century British polymath Joseph Priestley published A New Chart of History and its prose explanation as a supplement to his Lectures on History and General Policy. Together with his Chart of Biography (1765), which he dedicated to his friend Benjamin Franklin, Priestley believed these charts would allow students to "trace out distinctly the dependence of events to distribute them into such periods and divisions as shall lay the whole claim of past transactions in a just and orderly manner."

The Chart of History lists events in 106 separate locations; it illustrates Priestley's belief that the entire world's history was significant, a relatively new development in the 18th century, which had begun with Voltaire and William Robertson. The world's history is divided up into the following geographical categories: Scandinavia, Poland, Russia, Great Britain, Spain, France, Italy, Turkey in Europe, Turkey in Asia, Germany, Persia, India, China, Africa and America. Priestley aimed to show the history of empires and the passing of power; the subtitle of the Description that accompanied the chart was "A View of the Principal Revolutions of Empire that have taken place in the World" and he wrote that:

Carl Wilhelm Scheele (German: [ˈʃeːlə], Swedish: [ˈɧêːlɛ]; 9 December 1742 – 21 May 1786) was a German-Swedish pharmaceutical chemist.

Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified the elements molybdenum, tungsten, barium, nitrogen, and chlorine, among others. Scheele discovered organic acids tartaric, oxalic, uric, lactic, and citric, as well as hydrofluoric, hydrocyanic, and arsenic acids. He preferred speaking German to Swedish his whole life, as German was commonly spoken among Swedish pharmacists.

An ink eraser is an instrument used to scrape away or chemically bleach ink from a writing surface. This is a more involved process than removing pencil markings. Pencil marks can be gradually adhered to natural rubber fragments by rubbing the mark with a pencil eraser (this action is what prompted Joseph Priestley to give solidified latex its common name). Ink, however, readily penetrates the fibers of most papers and is therefore more difficult to extract by mechanical action.

Older ink erasers are therefore small knives designed to scrape off the top few microns of a sheet of paper, removing the ink that had penetrated. In concert with bladed ink erasers, an eraser similar to those at the end of pencils was also used, with additional abrasives, such as sand, mixed into the rubber. Fibreglass ink erasers also work by abrasion. These erasers physically remove the ink and the paper it has marked from the larger sheet.

The Test Acts were a series of penal laws originating in Restoration England, passed by the Parliament of England, that served as a religious test for public office in England and Wales, which imposed various civil disabilities on Roman Catholics and nonconformist Protestants. The underlying principle was that only people taking communion in the established Church of England were eligible for public employment, and the severe penalties pronounced against recusants, whether Catholic or nonconformist, were affirmations of this principle.

Although theoretically encompassing all who refuse to comply with Anglicanism in a dragnet approach, in practice the nonconformist Protestants had many defenders in Parliament and were often exempted from some of these laws through the regular passage of Acts of Indemnity: in particular, the Indemnity Act 1727 relieved nonconformists from the requirements in the Test Act 1673 and the Corporation Act 1661 that public office holders must have taken the sacrament of the Lord's Supper in an Anglican church.

Northumberland County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 91,647. Its county seat is Sunbury. The county is part of the Central region of the commonwealth.

The county was formed in 1772 from parts of Lancaster, Berks, Bedford, Cumberland, and Northampton Counties and named for the county of Northumberland in northern England. Northumberland County is a fifth class county according to the Pennsylvania's County Code. Northumberland County comprises the Sunbury, Pennsylvania Micropolitan Statistical Area, which is also included in the Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area. Among its notable residents are Thomas L. Hamer, a Democratic member of Congress in the 1830s, and Joseph Priestley, the Enlightenment chemist and theologian, who left England in 1796 due to religious and political persecution and settled on the Susquehanna River. His former house, originally purchased by chemists from Pennsylvania State University after a colloquium that founded the American Chemical Society, is a historical museum.