Refracting telescope, 1749-1783.
© Science Museum / Science & Society Picture Library
This small bras telescope was made in London by either Jonathan Sisons or his son, Jeremiah. The instrument has a 1 1/4 inch (32mm) lens and is carried on an equatorial mount of the Baker type first introduced by the Sisons. Used in conjunction with a table, the equatorial stand could be made horizontal using the three adjusting screws and the pair of spirit levels. Once adjusted, objects could be located using the circular setting scales and naked-eye sight. A telescope of this quality would only have been affordable to the wealthy amateur astronomer.