Music is one of the most familiar features of everyday life and in all cultures since time immemorial people have danced and sung in rituals, in celebrations, as an expression of joy, or just for fun. Whenever the pressure of the air is changed rapidly, by beating a drum, by rattling a stick in a tin can, or by plucking a string stretched across a box, our ear-brain system detects the pressure changes as sound. The sound travels from the source to the listener as sound waves, but what are they really like? And why are some sounds musical and others just noise? The answer that we shall find for simple, single sounds is fairly easy: if the vibration is very regular the sound is more musical than if it is irregular. But, as soon as we move to the more complex sounds and mixtures that occur in the real world of music, the difference is far less easy to describe in any scientific way. The answer to the question of why some combinations of sounds seem more pleasant to the ear than others is not easy to find. Some musical instruments (talking drums and trumpets of Africa) are used for sending information from one place to another. Is all music concerned with passing on information? Why do some people love a piece of music that other people hate? There are obvious differences in the musical likes and dislikes of people of different cultures and yet some people say that music is a universal language. How much of what we like is determined by our experience and upbringing and how much arises from the physics of the ear-brain system? What part does memory and conditioning play in our appreciation of music? Why do some sounds make us laugh and why can music have such a powerful effect on our moods? It is unlikely that we shall find very clear cut answers to these questions, nor indeed to the general question posed by the title of this lecture. But we should have a good deal of fun exploring the subject with experiments and recordings and, hopefully, we shall know a lit