Final answer:
The claim that the speed of light cannot travel along a wire of glass is false. Light travels at its maximum speed in a vacuum but it also can travel through other media like glass, where its speed is reduced due to refraction.
Step-by-step explanation:
The claim that the speed of light can travel in the vacuum of space but not along a wire of glass is false. Light indeed travels through vacuum and this is the medium where it reaches its maximum speed, approximately 3.00×108 meters per second (c). However, this does not mean light cannot travel through other media like glass. When light enters a medium such as glass or water, its speed decreases due to the material's optical density. For example, in glass, light travels at roughly two-thirds of its speed in a vacuum. As it changes mediums, the light also changes direction, a phenomenon known as refraction. The speed of light, therefore, does slow when it encounters a medium other than vacuum.