1S18.] Royal Scclcli/ of Edinburgh. 15 1 



salt. In confircnation of this opinion, Dr. Ure finds that both 

 common sal-ammoniac, and that condensed from the component 

 gases, attract moisture from the air to the amount of six or seven 

 per cent. The latter preparation, from its being more finely 

 comminuted than the other, becomes even pasty, when exposed 

 for a day to the humid atmosphere of this country. By the 

 cautious application of heat, this hygrometrical water may be 

 entirely expelled ; when the salt resumes exactly its pristine 

 Weight and dryness. Dr. lire's concluding experiment consists 

 in the transmission of dry muriatic acid gas over ignited turnings 

 of pure iron, when a portion of water or liquid acid, correspond- 

 ing in quantity to the proportion of muriate of iron formed, 

 always makes ,its appearance. The muriate of iron seems 

 peculiar. It is in small plates, or spangles, of a micaceous lustre, 

 and appears to contain a smaller proportion of iron, and that in 

 a lower state of oxidizement, than the common muriated black 

 oxide. The Doctor infers, from the whole of these researches, 

 that chlorine is oxymuriatic acid ; and that the hydro-chloric 

 gas of Sir H. Davy and M. Gay Lussac consists of an atom of 

 dry muriatic acid united to an atom of water, like gaseous 

 sulphuric and nitric acids. 



At the same meeting a paper by Dr. Brewster was read, on a 

 singular affection of the eye in the healthy state, in consequence 

 of which it loses the power of seeing objects within the sphere 

 of distinct vision. When the eye is steadily fixed upon any 

 object, this object will never cease to become visible ; but if the 

 eye is steadily directed to another object in its vicinity while it 

 sees the first object indirectly, this first object will, after a certain 

 time, entirely disappear, whether it is seen with one or both eyes, 

 whatever be its form or colour, or its position with respect to the 

 axis of vision. When the object is such as to produce its acci- 

 dental colour before it vanishes, the accidental colour disappears, 

 also, along with the object. The preceding experiments have no 

 connexion whatever with those of Mariotte, Picard, and Le Cat, 

 relative to the entrance of the optic nerve. In the course of this 

 investigation, Dr. Brewster was led to a new theory of accidental 

 colours, which will be read at a future meeting. 



In consequence of the very ample account of the proceedings 

 of the Royal Society of Edinburgh, the reports from the Geological 

 and Linnaean Societies are, of necessity, postponed to the next 

 month. 



