Kaiser Wiki

Objective lens diameter: 6.4“ Focal length: 102”

In the middle of the 19th century astrometry was a central activity for astronomers. So Kaiser ordered a state of the art instrument from the workshop of Pistor&Martins (Germany). It got a prominent place in the western room connecting the central building and the directors' house.
The roof and windows could be opened, such that the North-South meridian was freely accessible. A precision clock by Andreas Hohwü (Amsterdam) provide the time. The telescope was installed immediately after the building was ready in 1861. In 1866 an electric registration system was added.
The instrument stayed in operation until about 1955. Then is was moved to the Boerhaave Museum. After being on display for many years it is now (temporarily) stored.

The foundation of the telescope is still visible in the visitors center. East and West blocks supported the pillars between which the telescope tube moved. The North and South blocks carried the collimators during the calibration. The part far East was meant for the clock. In this way the instrument was one unit, separate from the building.
Meridiaankijker clip schoolTV

The Meridian telescope was a very accurate telescope. And in this facet, the coal cellar caused much grief. There was a plain systematic fault that plagued the results of the Meridian telescope. Only after a few years was the source of the fault discovered. Specifically that the coal cellar was filled every autumn. In the winter though the coal was used until the basement emptied. Because the basement was not located at the center of the Observatory, the whole building slanted slightly as the coal was stocked up. As the basement emptied though, the building rose again. This effect could be seen in the measurements made with the Meridian telescope. This explained the systematic fluctuation in the observations.

It was with the Meridian telescope that the positions of the stars were measured. To make these observations, the observer who would read off the declination had to lean against the pole that supported the telescope. As a result, the body temperature of the observer would warm one side of the pole so that the telescope once again slanted in one direction. This naturally influenced the measurements. Now this was not so terrible if the telescope always leaned for the same amount because then it could be corrected for at a later point. However, when the observer left his post for a coffee break, for example, the pole would cool and the offset would differ. It was for this reason that the job of pole-warmer was instituted. The only thing that the pole-warmer had to do was to make sure to keep the pole warm throughout the night’s observations.

[]Next to the entrance of the building we cna find a marker with a cross on it. This is is official meridian reference point of Leiden from which the time would be measured. Notice that the transit circle does not reside on this spot, but a few meters west of it. The New Amsterdam time was measured from this spot.