Meridian circle, Pistor & Martins, Berlin, 1860
Inv V03471

As early as 1740 the Leiden Observatory had the use of a meridian circle or passage circle. This had been acquired by 's Gravesande. A meridian circle is a telescope which turns in an exact North-South plane. As a result you see the sun only when it is at the highest point of the day. The apparatus was used mainly for measuring time. When the sun is at its highest point it is exactly 12 noon. In this way all the clocks in the observatory could be set to the correct time. This was repeated every day (at least if the sun was shining). The clocks were usually adjusted only once a week, because of the work entailed. For the rest of the week people worked with a written correction.Frederik Kaiser took charge of the observatory in 1858 and acquired this meridian circle. The circle was installed in the new observatory in Leiden, next to the Botanical Garden.