B. TERRESTRIAL PHYSICS AND METEOROLOGY. 87 



defective nature of our observations. The cumulus is rare in 

 winter, and abundant on hot summer days. It disappears 

 periodically in the dry winter season in the climate of the 

 city of Mexico. The constitution of clouds is intimately de- 

 pendent on the intensity of the heat, and there are but two fun- 

 damental types the cold cirrus or cirro-stratus, and the warm 

 rain-clouds, the cirro-cumulus or pallium. 6 ^, 1873, 823. 



THE STOEMS OF NOKTHERX EUROPE. 



There has just come to hand a memoir by Hildebrandsson, 

 recently printed, but presented some two years ago to the 

 scientitic society of Gothenburg. 



The author's work consists in the special study of some se- 

 vere storms of Northern Europe, and he states that his object 

 has been not to combat any previous theory, but, on the con- 

 trary, to give as far as possible, independently of any previ- 

 ously conceived opinion, a contribution from Sweden to the 

 fund of facts upon which every theory ought to be estab- 

 lished. The accurate hourly observations made at Upsala 

 have proved of great value to him in his studies. 



His conclusions are summed up by himself as follows (and 

 that thev are so nearlv accordant with the laws of other inves- 

 tigators in America, in Europe, and India, would seem to argue 

 that the same causes operate in the same manner through- 

 out the world to direct the origin and progress of storms) : 

 Hildebrandsson says that the study of weather charts shows : 



1. Regjions exist of hisjh and low barometer, which are sur- 

 rounded by isobarometric lines of a more or less regular form. 



2. The isobars surrounding the areas of maximum barome- 

 ter are further separated from each other, the winds are fee- 

 bler and variable, and the sky is generally serene ; these are 

 thus the centres of fine, calm weather. 3. On the contrary, 

 around the lowest barometer the isobars are more crowded 

 together (at least on one side), the wind is stronger in propor- 

 tion as the isobars are nearer, and the direction of the w^ind 

 is determined at any point by the law of Buys Ballot, so that 

 the air seems to move about the centre of depression in a di- 

 rection contrary to the movements of the hands of a watch. 

 At the very centre itself is sometimes found a region where 

 the isobars are further separated from each other, and w^here 

 consequently the winds are feeble. 4. All the centres of de- 



