List the salient feastures of heat radiations.

Answer

### Step-by-Step Solution:

1. **Travel Through Vacuum**: Heat radiations can travel through a vacuum, which means they do not require a medium (like air or water) to propagate. This is a unique characteristic that distinguishes them from conduction and convection.

2. **Fixed Velocity**: The speed of heat radiation is constant and is approximately \(3 \times 10^8\) meters per second (the speed of light in a vacuum). This fixed velocity is crucial for understanding how quickly heat can be transferred over distances.

3. **Straight Line Propagation**: Heat radiations always travel in straight lines. This means that if there are no obstacles in their path, they will continue in a straight direction without bending.

4. **Obey the Law of Reflection**: Heat radiations follow the law of reflection, which states that when a ray of radiation strikes a reflective surface, the angle of incidence (the angle at which it hits the surface) is equal to the angle of reflection (the angle at which it leaves the surface). This is similar to how light behaves.

5. **Intensity and Distance Relationship**: The intensity of heat radiations is inversely proportional to the square of the distance from the source. This means that as you move further away from the source of heat radiation, the intensity decreases significantly. Specifically, if you double the distance, the intensity becomes one-fourth.

### Summary of Salient Features:
- Heat radiations can travel through a vacuum.
- They travel at a fixed velocity of \(3 \times 10^8\) m/s.
- They propagate in straight lines.
- They obey the law of reflection.
- Their intensity is inversely proportional to the square of the distance from the source.