PHYSIOGRAPHY OF THE AUSTRALIAN ALPS. 369 



6,000 feet, and there remained like a wide expanse of silvery- 

 ocean during the clear moonliglit night, until dissipated by the 

 warm golden rays of the rising sun. A peculiar feature of such 

 fogs is that tlie upper part is cooler than the lowei", i.e., when the 

 fog-masses are rising radiation of heat is greater at the upper than 

 at the lower part. 



As a rule, the number of cloudy days is in excess of the clear 

 days for the entire year, and tlie cloudiness is greater during 

 summer and winter than in spring or autunni. The beautifully 

 clear days of winter are a noticeable feature in tlie climate of the 

 Australian Alps, although frequently preceded by hard frosts, and 

 occasionally followed by heavy snow falls. 



The month of July is one of severe frosts in the Australian 

 Alps. At elevations of 2,000 feet, the frosts range from May to 

 September, but as the seasons are later at the sub-alpine habitats 

 than in the lowlands, the September frosts, which might prove 

 injurious to vegetation in the lowlands, are not so much so at these 

 elevations. 



It is only in the valleys that the severest frosts take place. I 

 have observed lowland exotic plants flourishing on the ridges, 

 which perished under the extreme frosts in the valleys, the 

 temperature being more equal at the former habitat than in the 

 latter. 



The range of temperature at sub-alpine elevations, as at Omeo, 

 2,20U feet, is appai-ently large and increases witli the elevation. 

 The annual mean temperature at Omeo, deduced from observations 

 extending over six years, gave 53.34°. The highest recorded 

 temperature in the shade, on 21st January, 1880, was 105° ; and 

 the lowest in July, 1883, 19° Fahrenheit, or 13° below freezing 

 point ; or an absolute range of 128° ; nearly as large as Chicago, 

 Illinois.* 



The mean annual temperature in the sun at Omeo was 63.38°, 

 a little over 10° higher than in the shade. 



The vai'iation to which the law of decrease of temperature 

 with elevation is subject, is well shown by many localities in the 

 Australian Alps, particularly by the presence of many tropical 

 types of vegetation in the humid soils on the most southern 

 slopes, at elevations of 3,000 feet ; and the mean temperature is 

 probably greater at similar elevations on the northera sunny 

 slopes, than on the moist southern slopes ; and the absolute range 

 of temperature is also greater on the former than on the latter at 

 .similar elevations. Again, those localities open to the cooling 

 influence of polar winds, would doubtless show a lower mean 

 annual temperature than those localities on the same latitude, at 

 the same elevation, although exposed to the warming influence of 

 equatorial winds. 



* Looniis' Meteorolog}', p. 274. 



