210 Scientific Intelligence. — Meteorology. 



as if by transmission, that is to say, perpendicularly as to the 

 planes of incidence, of reflection, or of transmission, — so far 

 coinciding. I shall conclude by remarking, that the planes of 

 glass being superimposed one on the other, we can easily give 

 to the mixed plate a suitable thickness, by turning the two 

 glasses upon each other with a moderate pressure, and by heat- 

 ing them. 



F. S. I moreover add, that the colours of mixed plates do 

 not need, like those of the more ordinary rings, to be placed 

 at the precise distance of distinct vision ; that the two inter- 

 fering rays not possessing the same intensity, there cannot be 

 the complete destruction of any colour, which is equivalent to 

 the declaration that all the tints are more or less mixed with 

 white ; and that, finally, as it regards the reflected rings of 

 mixed plates, the centre is white, the very opposite of what is 

 observed in ordinary rings, on account of the known loss of 

 a semi-interval of interference. 



2. Influence of the Height of the Barometer on the Level of the 

 Sea. — At Stockholm, it is a circumstance generally noticed by 

 the people, that, when the water in the harbour, which is a 

 bay of the north sea, stands low, so that the water of the 

 Malar Lake, which has almost the same level with the mean 

 height of the North Sea, has free exit, the air is clear and dry ; 

 and when the reverse is the case, so that the North Sea flows 

 into the Malar, wind aiid rain may soon be expected. This 

 circumstance was investigated by N. G. Schulten, who, after 

 he had ascertained the truth of the belief, proposed the fol- 

 lowing explanation, in the Transactions of the Royal Aca- 

 demy for 1806, p. 77 ; — ^that when the height of the barome- 

 ter, that is, the pressure of the air, is inconsiderable over this 

 part of the North Sea, but higher over another, the equilibrium 

 will be more speedily restoi'ed by water than by air, for this 

 reason, that the latter cannot give way to a higher pressure, 

 but must flow away ; whereas the elasticity of the air restores 

 the equiUbrium in this manner very slowly, owing to the por- 

 tions of air in contact with each other, of unequal pressure, 

 having so slight a diiference in pressure, that it is almost un- 



