Prof. Forbes on the Vibrations of heated Metals. 15 



My experiments, however, would seem to be fuller and 

 more complete than the original as mentioned in the Encyclo- 

 pfedia, as I had injected the choroides minutely, dissected it 

 out, and washed it carefully to remove the pigmentum. This, 

 however, is of no moment, excepting as regards the object I 

 had in view. 



If Sir David Brewster has happened to see the Essay 

 I published last year, on the subject of a new membrane in 

 the eye, he will find that my object has been to prove that 

 the anatomy of the choroid membrane in animals has not 

 been hitherto thoroughly understood ; that the brilliant colours 

 we meet with in the eyes of various animals, which we have 

 been accustomed to consider as appertaining to a peculiar 

 secretion of the choroid tunic, and which, it may be easily 

 seen, are so stated to be in standard anatomical and physio- 

 logical works* even to this day, — that these brilliant colours 

 are not owing to any such secretion, but arise from the peculiar 

 construction of the anterior lamina of the choroid membrane 

 which I have ventured to term the Membrana versicolor. 



That the membrana versicolor is perfectly distinct from the 

 choroides is, I think, satisfactorily shown by direct experiment, 

 and perhaps particularly so by the one above mentioned, in 

 which the eye of the sheep was minutely injected. 



In conclusion, I may remark that this curious fact, as re- 

 gards the experiment first named, does not invariably hold 

 good. We find the colours disappear by drying, and reap- 

 pear by moistening, in the sheep, ox, &c, but it will not do so, 

 completely, in the cat, and probably not in the fox or the lion. 

 The reason of this is the much greater thickness of the mem- 

 brane in these animals. 



I hope shortly to have some remarks on Vision to offer. 



I am, Gentlemen, yours, &c. 

 Hull, Oct. 14, 1833. Geo. H. Fielding. 



VII. Experimental Researches regarding certain Vibrations 

 which take place between Metallic Masses having differ cut 

 Temperatures. By James D. Forbes,^., F.li.SS. L. fy Ed. 

 Professor of Natural Philosophy in the University of Edin- 

 burgh^. 



1- (~) N tl't 17th of January 1831, Mr. Arthur Trevelyan 

 ^^ communicated to the Itoyal Society of Edinburgh a 



* As Hell, Fyfe, Bostqck, Cuvier, Hunter, &c. 



ffroin the Transactions' of the Royal Society of Edinburgh, vol. xii. This 

 paper was read before the .Society on the 18th of March and 1st of April 1833. 



