172 



nation ; no embryonic cell was observed before it began, nor in any 

 of the cleavage masses. 



The inner membrane is folded in during cleavage; it is easily 

 seen thrown into folds at the cleft, and for this reason I do not 

 consider it a yelk-membrane, which term would be better applied to 

 the chorion. 



II. " On the Applicability of Gelatine Paper as a Medium for 

 Colouring Light." By HORACE DOBELL, Esq. Communi- 

 cated by JAMES PAGET, F.R.S. Received November 9, 

 1854. 



The object of this communication is threefold. 



(1.) To point out the properties of a material called Gelatine 

 Paper, which render it applicable as a medium for colouring light. 



(2.) Through the means of gelatine paper, to introduce the use 

 of coloured light in the arts for the preservation of the sight of 

 artisans. 



(3.) To introduce the use of gelatine paper for the relief of 

 persons suffering from impaired vision ; for the preservation of the 

 sight of travellers, and of all those who are much engaged in reading. 



This material was invented in 1829 by the late M. Grenet, of 

 Rouen, and was exhibited by him in its present state of perfection 

 at the Great Exhibition of 1851. But up to the present time it has 

 not been successfully applied to any more useful purposes than the 

 manufacture of artificial flowers, address-cards, tracing-paper, wafers, 

 wrappers for confectionary, and the like. 



It is commonly manufactured in sheets, measuring 22 inches in 

 length and 16 inches in diameter, which are sold at a small price; 

 but the sheets can as easily be made of any dimensions not ex- 

 ceeding those of which plate-glass is capable. It can be made of 

 any thickness, from that of the finest tissue paper upwards. It may 

 be obtained as transparent as the best glass, and more free from colour, 

 or of all colours and shades of colour, without interfering with its 

 transparency. It is exceedingly light, and may be bent or rolled 

 up without injury. It can be cut with scissors like ordinary paper, 



