The instrument listed in the inventory under number 3429 was analyzed in particular. Both the mechanical part and the optical part were studied, applying four methods of investigation:
- 1) photography;
- 2) endoscope examination;
- 3) radiographic examination;
- 4) microphotography.
According to Allodi, "We may conclude that No. 3429 is a true Galilean microscope, which combines the perfected features of the other models of the time, although for its fabrication Galileo would have made use of the services of specialized workers in iron, paper, and wood, as well as goldsmiths, as was necessary and customary at the time."
This important instrument is still today indicated as "Galilean microscope", although more recent studies show that the famous instrument-maker Giuseppe Campani (1635-1715) should probably be credited with its construction. Accordingly, it was probably fabricated in the second half of the 17th century.