Fig. 27 Fig. 28
See also Figures 1, 2, 3, 6, 7, 8, 9 and 10.
Leonhard Zubler's 'geometrical gunnery instrument' did not have the pretensions to universality of the 'proteo militare' but was still expected to fulfil a range of roles. Like several other contemporary devices (catalogue nos 7, 60 and 64), Zubler's instrument had two jointed legs attached to a central leg, with smaller supporting limbs providing additional links between the central and side legs. In Zubler's version, the supporting limbs slide in a slot in the central leg when the angle between the side legs is altered. The slider moves against a scale of degrees to indicate the angle so that, with a plumb bob and line, the instrument can take the place of a gunner's quadrant. Gunner's gauge and inch scales enable the device to act as a pair of measuring calipers, and Zubler discusses the size and weight of shot and quantity of powder for both long guns and mortars, as well as the ranges they achieved.
As with Zubler's other tracts on new instruments (e.g. catalogue nos 54 and 58), the volume is liberally illustrated with finely executed copper-plate engravings. Zubler was well aware of the visual appeal and distinction of his publications and typically advertised the engravings on his title pages - in this case we are told that the book comes with 'schönen kunstreychen Kupfferstucken'. Among the illustrations are several showing gunner's sights in use. The sights are mounted at the breech end of cannon and have a sliding pinhole moving in a slot against a scale. The gunner set the required elevation on the sight and then adjusted the inclination of the gun until the pinhole, target and top of the gun's muzzle came into alignment.
Although the focus of the text is on gunnery, the book's final section deals with the more general uses of the instrument, especially in mensuration and surveying. To aid in such work, the instrument carries a compass. Zubler also mentions in passing that the instrument can in principle be used for astronomical observations.
At the end of the book is an advertisement for the instruments available from Zubler, who lived and worked in Zurich. Artillery instruments are grouped along with sundials, astrolabes, quadrants, nocturnals and sectors, indicating that gunnery instruments were here firmly identified as mathematical instruments.