In Captain Parrys third polar expedition, Lieutenant Forster held a conversation across the harbour of Port Bowen, the distance being a mile and a quarter.

63 The intensity of sound is affected, also, by its original direction, and by the nature of the surface over which it passes.

It is greatly lessened, when the sound is transmitted through media of different conducting power.

Hence, the destruction of the homogeneity of the air, by alteration of temperature, is unfavourable to the transmission of sound -: and it is transmitted better by night than by day.

Hence, also, a tall glass half filled with champagne, cannot be made to ring, as long as the effervescence continues, 64 Sounds are diminished in intensity, by passing from solid to fluid, and still more to gaseous substances.