Introduction

The machine

The story

Static history

The challenge

For teachers

Priestley's Electrostatic Machine

 In the mid-eighteenth century, an interest in electrostatics was very fashionable. The well-off would not only attend lectures but buy the books and equipment to copy  the demonstrations they had seen in the lectures. Take a good look at this engraving, from a book by William Watson (1748). A simple hand-driven machine provides the electrical charge. A very popular demonstration was to hang small boys by silk ropes and charge them electrically. Their hair would stand on end and sparks might fly to anyone who stood near. In the background are two bells that would ring under the influence of electricity. The young girl also receives electrical charge. Another popular demonstration was to let charge build up in a young girl and invite members of the audience to experience an 'electrical kiss.' The whole thing became 'the latest trend,' and good money could be gained by electrifying people in fair grounds. People thought that being electrified was good for their health.  In the picture above, a man turns the handle on the machine which turns a glass globe. The woman assistant holds her hand against the spinning globe to 'produce' static by the action of friction. The boy's feet also appear to rub against the globe. What happens when the boy and girl touch hands? Why is the girl standing on a barrel? What is the girl looking at? Study the picture then try our matching exercise. the machine shown below was designed and built a little later than the scene above and for a much more serious study of electricity.

The need for an assistant has been dispensed with. Instead a pad is used to rub against the glass. We now know that electrons would have been rubbed from the glass onto the pad, making the glass positively charged and the pad negatively charged. Of course this was a long time before electrons were known about, but the words positive and negative were used.

However what makes the machine so very special is not so much its construction but that it was almost certainly designed, commissioned and used by a most remarkable scientist: Joseph Priestley. A man who made huge contributions to science.

The machine would have been made at about the time that Priestley wrote 'History and Present State of Electricity'. In this book he describes a timeline of discoveries in the the area of electrostatics and suggests a few ideas of his own. To find out more, read about Static history or Priestley's story.