Canal rays travel in a straight line.

Answer

**Solution:**

Canal rays, also known as anode rays, were discovered by the German scientist Eugen Goldstein through his experiments with a discharge tube. Here’s a step-by-step explanation of why canal rays travel in a straight line:

1. **Understanding Canal Rays**: Canal rays are streams of positively charged particles (often protons or other ions) that are produced when a high voltage is applied across a discharge tube containing a perforated cathode.

2. **Goldstein's Experiment**: In Goldstein's experiment, he applied high voltage across a discharge tube that had a cathode with holes. When the voltage was increased to several thousand volts, a faint red glow was observed emanating from the holes in the cathode.

3. **Nature of Canal Rays**: The rays that emerged from these holes were identified as canal rays. These rays consist of positively charged particles that move towards the negatively charged cathode.

4. **Behavior in Absence of Fields**: When canal rays are observed in the absence of electric and magnetic fields, they travel in straight lines. This behavior can be attributed to the fact that there are no external forces acting on the charged particles to deflect their path.

5. **Conclusion**: Therefore, canal rays travel in a straight line because, without the influence of external electric or magnetic fields, the positively charged particles continue on their path unimpeded.

---