The beam isn't carrying. Something's blocking it.
2 seconds sound clip from Superman (1948) - The Reducer Ray (Chapter 3).
You can hear this line at 00:10:06.523 in the Blu-ray version of the episode.
Quote context
[...]
- I'd like to test the negative rays this gun gives out before I turn them against the Reducer Ray.
- Here comes a train, why don't you try and stop it?
- That's a good idea. I'll experiment on that.
- I'll bet that engineer will never figure out what stopped his train.
- Now we're ready for the Reducer Ray.
- The beam isn't carrying. Something's blocking it.
- Crandall calling Spider Lady.
- You can understand the danger which would threaten the world if it fell into the wrong hands.
[...]