While the exact invention of the ceilometer is difficult to pin down, it's generally credited to François-Ernest Guyon, a French meteorologist.

Here's why:

* Early Designs: Guyon's work in the early 1900s focused on developing methods to measure cloud heights. His early "célimètre" used a searchlight to project a beam of light upward, allowing an observer to measure the distance to the clouds based on the angle of the beam.

* Evolution of the Ceilometer: Over time, other researchers and companies built upon Guyon's work. Developments like the use of lasers, rotating beams, and automated sensors led to the modern ceilometers we know today.

Therefore, while Guyon may not have invented the *final* form of the ceilometer, his work laid the foundation for the development of this crucial meteorological instrument.