Page:Hunt - The climate and weather of Australia - 1913.djvu/133

Rh Synchronous observations are received by telegraph from a number of stations from as wide an area as possible.

The following table gives the number and equipment of stations reporting daily to the Central Bureau:—

The barometer readings after being reduced to sea—level, to freezing point, and for standard gravity, are plotted on a separate chart, together with wind direction and wind velocity.

All readings of the same height are then connected up by lines or isobars, thus we have invariably presented on the charts a number of contour curves which represent graphically the different pressures of the atmosphere prevailing over those portions of the earth's surface under review.

Other secondary charts are also compiled for discussion. On one is shown by figures and shading the synchronous weather throughout Australasia, the amount of cloud, rain recorded, and temperatures; on a second, the variations of pressure for the 24 hours, which indicate in a measure the probable direction of atmospheric drift; on a third, the variation in temperature for the same interval of time, and this is useful in suggesting the probable route of hot and cold waves.

All these factors are discussed together with the conditions assumed to be normal for the time of the year, and from them the forecast deductions are made.