Final answer:
Janssen most likely believed that light bounces off surfaces during the time of his invention.
Step-by-step explanation:
Janssen most likely believed that light bounces off surfaces during the late 1500s when he invented the microscope. This is because he observed the reflection of light off objects through the lens of his microscope. Light reflection is a property of light that allows us to see objects and form images.
Learn more about light reflection