Reflecting telescope: Newtonian; seven foot

This large reflecting telescope was made by the English astronomer William Herschel and was bought by Teylers Museum in 1790. The telescope was made after a design of the English physicist Isaac Newton. Via a mirror system the image is led to the ocular, the viewing part. The ocular is the short copper tube perpendicular to the telescope barrel. In the ocular is a lens which magnifies the image. As the size of the mirror determines the strength of a telescope, Herschel wanted to build a telescope with a mirror as large as possible. For the larger the mirror, the more light it will catch and the more celestial bodies can be seen. However, when the mirror is larger, the telescope barrel has to be larger too. Therefore, this telescope has an octagonal barrel of no less than seven foot long. Because there were hardly any large mirrors at that time, Herschel perfected the technique to make mirrors. They were not only large, but also of an excellent quality.