1820.] Philosophical Transactions for 181&, Partll.andlll. 51 



sideration the air which exists in such abundance in the pores 

 of the body. 



IX. A71 Account of a Membrane in the Eye, now first described. 

 By Arthur Jacob, M.D. Member of the Royal College of Sur- 

 geons in Ireland, Demonstrator of Anatomy, and Lecturer on 

 Diseases of the Eye in the University of Dublin. 



It has been the general opinion of anatomists, -that the retina 

 consists of two portions or membranes ; 1, an expansion of the 

 nerve, next the choroid coat ; 2, a vascular layer next to the 

 vitreous humour. It is generally admitted that the medullary 

 expansion of the nerve cannot be separated so as to present the 

 appearance of a distinct membrane, though it may be scraped 

 off, and even portions of it detached, leaving the vascular layer 

 perfect. Dr. Jacob has found that besides these two layers the 

 retina is covered on its external surface by a delicate transparent 

 membrane united to it by cellular substance and vessels. This 

 structure, not hitherto noticed by anatomists, he has had so 

 many opportunities of demonstrating as to leave no doubt whatr- 

 ever of its existence. He considers it as a distinct and perfect 

 membrane, apparently of the same nature as that which lines 

 serous cavities. He describes at full length the method of 

 demonstrating it. 



The author terminates his paper by observing that the different 

 coats of the eye are not merely in contact, but are likewise 

 united together by cellular substance and delicate vessels. 



X. A new Method of solving numerical Equations of all Orders 

 by continuous Approximation. By W, G. Horner, Esq.— I 

 regret that it is inconsistent with the plan of this work to give 

 an analysis of this valuable and ingenious papef here. The 

 reader will find it well deserving his attention. 



Philosophical Transactions of the Royal Society of London 

 for the Year 1819, Part III. 



This part contains only a single paper ; namely, 

 An Account of Experiments for determining the Variation in 

 the Length of the Pendulum Vibrating Seconds at the principal 

 Stations of the Trigonometrical Survey of Great Britain. By 

 Capt. Henry Kater, F.R.S. — In the year 1816 an address was 

 presented by the House of Commons to the Prince Regent 

 praying him to give directions for ascertaining the length of the 

 pendulum vibrating seconds of time in the latitude of London as 

 compared with the standard measure in the possession of the 

 House of Commons, and for determining the variations in the 

 length of the said pendulum at the principal stations of the trigo- 

 nometrical survey, extended through Great Britain. In conse^ 

 qnence of this address, an application was made by his Majesty's 

 ministers to the Royal Society, requesting the assistance of that 

 body. A committee was appointed for the purpose, and Capt. 

 Kater was selected to make the experiments. 



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