266x brass

Magnification 266x | Aperture in plates 1.06 mm
Body plates 45 mm x 25 mm | Pitch of main positioning screw 0.66 mm

This microscope was #3 in van Zuylen and Bracegirdle. It was #60 in Harting's catalogue of the 1875 exhibition.

It has been in the collection of the University of Utrecht, now in the Universitietmuseum, since the early 1800's.

The magnification of the lens in this microscope makes it the strongest of the suviving eleven, though the eleventh, measured at 248x is very close behind. These two are the strongest by far compared to the other ten. They are stronger than the 26 that Leeuwenhoek bequeathed to the Royal Society, now lost, measured by Baker in 1739 as magnifying between 40x and 160x. They are also stronger than the five eel viewer lenses in the Boerhaave, measured for the 1982 exhibition as magnifying between 30X and 161x.

These two, the one in Utrecht and the newly disovered eleventh, are the only two lenses that give evidence of having been blown from hot glass rather than having been ground from a cold shard. Stronger was not always better. For many of Leeuwenhoek's observations, lower-powered microscopes were more appropriate for what he wanted to see. He wrote on June 9, 1699, to the Royal Society:

When we now observed this creature through the Magnifying glass which we considered most suitable for it ...

Like the 112x and 110x brass microscopes on the left sidebar, this microscope has an extra hole in the L-bracket, perhaps for the same reason.

In 1850, it was mentioned by Harting in the third volume of his Het Microscoop (1850), p. 43) and was exhibited in Delft in 1875.

It is also discussed in Van Cittert's Descriptive catalogue (pp. 14–6), which has an introductory historical survey of the resolving power of the microscope, and in Brian Ford's Leeuwenhoek Legacy (pp. 149–51).