On the Culuured Uuuppes or Sectors of Haidinger. 323 



18. On this theory, then, the semidiurnal oscillations are 

 supposed to be occasioned by two vast waves perpetually moving 

 round the earth, almost like the tides of the ocean. Air of 

 of course would not be carried round by these waves, but a 

 general swaying to and fro of the upper parts of the atmosphere 

 would be the only actual motion occasioned. The waves origi- 

 nate in the sun throwing the air on each side of him ; hence 

 there must be a constant tendency to an easterly wind before 

 noon, and a westerly wind in the afternoon. 



These daily barometric waves are of greatest height and regu- 

 larity in the equatorial regions, and are not appreciable in the 

 polar regions*. The varied shape of oceans, continents, and even 

 mountain-chains must produce irregularities, and the change of 

 seasons must occasion modifications of the wave-curve, to dis- 

 cover and explain which will afford employment to numberless 

 students of meteorological science for many years to come. 

 Eventually we may hope that an endless variety of facts, only 

 apparently capricious, will be made to harmonize together under 

 a simple mechanico-mathematical theory, and the science of the 

 atmosphere will be raised to a new position. 



Sydney, New South Wales, 

 January 10, 1859. 



L. On the Coloured Houppes or Sectors of Haidinger. By 

 Sir David Brewster, K.H., D.C.L,, F.R.S., and Foreign 

 Associate of the Institute of Francef. 



lYI IIAIDINGER;S fine discovery of the coloured houppes 

 1t± • or sectors which are visible in polarized light, and indi- 

 cate its plane of polarization, is one of great interest both in its 

 optical and physiological relations. Having always believed that 

 they were produced by a peculiar structure in the eye, placed 

 between the vitreous humour and the sclerotic coat, I could not 

 adopt the ingenious explanation of them given by M. Jamin, 

 and I have therefore been induced to examine them with some 

 care. 



In order to discover their cause, we must ascertain their size, 

 their form, their colour, and the intensity of their light. 



1. In reference to their size, M. Haidinger states that each 

 has " an apparent diameter of nearly two degrees," that is, four 



* It is probable that, during the passage of the sun, a certain overflow 

 of air wouhl take i)lace from the equatorial and temperate upon the polar 

 regions, followed by a corresponding reflux. An inversion of the barome- 

 tric curve would hence result in the polar regions, such as is thought to 

 occur. (See 'Cosmos,' Sabine's translation, vol. i. p. ,'W9.) 



t Communicated bv the Author. 



