328 Proceedings of the British Association for 1850. 



for quantity, which he considered superior to his own. The 

 distance the paper passes over now shews the quantity of 

 air which passes in a given time. For example, one inch of 

 paper represents ten miles of air. A clock strikes off the 

 hour on the paper. By these improvements we are enabled, 

 by one line, to observe the direction of the wind, the length 

 of the current passing, and the time of passing. It is very 

 desirable to have observations on larger areas, or over greater 

 ranges. On arriving in Edinburgh, he found different cur- 

 rents indicated at the Calton Hill from those at Birmingham 

 on Tuesday last. The great currents of the atmosphere 

 should be first traced all over the earth's surface, and after- 

 wards those more local. 



Mr John Tyndell then read a paper on the Magneto-Optic 

 Properties of Crystal. 



Mr J. A. Broun presented four papers on magnetic forces. 



Mr Broun next read a paper on the construction of the 

 suspension threads of the declinometer. 



Sir D. Brewster gave a short notice on the polarising 

 structure of the eye. He referred to the phenomenon called 

 Haidinger's Brushes. These discoveries prove three different 

 polarising structures in the eye, — in fact that the eye may 

 be a polariscope. It was difficult to see the brushes. Neither 

 he nor Haidinger can explain .the cause of this property. — 

 Professor Stokes had also a communication on the same sub- 

 ject. He had seen the brushes with great facility ; and he 

 described their appearances as seen under various circum- 

 stances, and at various positions of the spectrum, having 

 traced them over several of Fraunhofer's lines. 



Rev. C. F. Lyon on some phenomena of Mirage on the East 

 Coast of Forfarshire. 



Mr Roberts detailed some experiments on the expansion 

 of glass, wood, and metals, from changes of temperature. 



Section B. — Chemistry. 



" On a new and ready Process for the Quantitative Deter- 

 mination of Iron,'' by Dr F. Penny. — The author recommends 

 the employment of the chromate and bichromate of potash 

 for the estimation of iron in the common ores of the metal, 



