When did scientists first discover that light had a specific, measureable speed?

Around 1676,danish astronomer Ole Roemer became the first person to prove that light travels at a finite speed

How is it possible that phylogenies based on sequences from nuclear genomes and organellar genomes (i.e., chloroplasts and mitochondria) from the same group of species yield phylogenetic trees with different branching orders?   answer :   the genome of the endosymbiont is more closely related to members of the group in which it originally evolved, while the nuclear genome of the engulfing organism has its own evolutionary trajectory.