21 6 PHILOSOPHICAL TRANSACTIONS. [aNNO 1668. 



live coal and shining wood is this, that although the light of the former is 

 readily extinguishable by compression, the latter is not affected by it. — 2. A 

 live coal will in a very few minutes be totally extinguished by withdrawing 

 the air ; whereas shining wood immediately recovers its light if the air be 

 admitted again, even though excluded for half an hour. — 3. A live coal 

 being put into a small close glass, continues to burn only a very few minutes ; 

 but a piece of shining wood continues to shine for whole days. — 4. A coal as it 

 burns emits a great deal of smoke or exhalations ; but luminous wood does not 

 so. — 5. A coal in shining wastes at a great rate ; but shining wood does not. — 

 6. Live coal is actually and vehemently hot ; whereas shining wood is not sen- 

 sibly lukewarm. 



An Ohservatmi concerning a Blemish in a Horses Eye, not hitherto 

 discovered by any Author. By Dr. Rich. Lower. N° 32, p. 613. 



The eyes of horses are peculiarly affected with a disorder which no animal 

 besides is troubled with, as far as I have observed ; neither do I remember any 

 author hitherto to have taken notice of it. It is a spungy excresence (com- 

 monly of a dark musk colour) which grows out of the edge of that coat of the 

 eye called the uvea ; which spunge if it grow large or increase in number (as 

 frequently happens) it depraves the sight very much, or totally intercepts it. 

 But that you may more easily conceive the manner how it is done, you may 

 remember that the uvea is a muscular part, the use of it being chiefly to con- 

 tract and dilate itself for the admission of objects with as much light as the eye 

 can conveniently bear ; so that the brighter and more refulgent the light is to 

 which the eye is exposed, that membrane contracts itself into a narrower 

 compass ; and the darker the place is the more it dilates itself, as you may see 

 most readily in a cat's eye : so that if that spungy substance which grows out 

 of the edge of the uvea be so great, or the number of them such as that they 

 grow in several places about the pupil of the eye, where it contracts itself, the 

 pupil or sight is very much (if not totally) obstructed, and consequently the 

 horse sees very little or nothing at all : as I have many times taken exact notice 

 in some horses, which being brought into the sun-shine, could not see at all, 

 but suffered me to touch the sight of their eye with my finger without the least 

 winking ; which horses being led back into the stable, the uvea in that obscure 

 place dilating itself, they could see very well again, and would not suffer me to 

 show my finger near to the eye without frequent closing their eye-lids and 

 tossing their heads. The same horses I understood by the owners were very 

 apt to stumble in the day-time if the sun shone, but travelled very well and 

 securely in the evening and in dark cloudy weather. 



