QS Proceedings of Philosophical Societies, [JuLt, 



azote and carbonic acid ; about 94 of the former, and 6 of the 

 latter. 



For the purpose of elucidation, Dr. Davy described the results 

 of a number of experiments which he had made on dogs, prov- 

 ing that different gases introduced into the pleura are absorbed 

 with different degrees of rapidity. Nitrous gas, nitrous oxide, 

 oxygen, and hydrogen, soon disappearing, carbonic acid gas 

 more slowly, and azote slowest of all. 



Some of the experiments gave rise to the idea that azote was 

 effused into the pleura by the secernent arteries. This subject 

 is discussed by Dr. Davy in connexion with the consideration of 

 the air occasionally found by anatomists in difierent parts of the 

 body. This air, for reasons which he assigns, he thinks is azote. 

 He does not believe that it is carbonic acid gas, because he has 

 been able to detect the slightest traces of this acid in blood 

 either by means of a high temperature, or the vacuum of an air- 

 pump, and because blood contains alkali not saturated with this 

 acid, and is able, in consequence, to combine with an additional 

 portion of it. 



At this meeting a paper was also read, on Fossil Shells ; by 

 L. W. Dillwyn, Esq. FRS. in a letter to the President. 



This paper principally related to the geological distribution of 

 turbinated univalves. 



At this meeting likewise, the reading of the following paper 

 was begun : Observations and Experiments on the Daily Varia- 

 tion of the Horizontal and Dipping Needles, under a reduced 

 directive Force ; by Peter Barlow, Esq. of the Royal Military 

 Academy, FRS. elect. (Communicated by Davies Gilbert, Esq. 

 Treas. RS.) 



June 12. — The reading of Prof. Barlow's paper was resumed 

 and concluded. 



A century has now elapsed. Prof. Barlow observed, in the 

 commencement of this paper, since Mr. Graham discovered the 

 diurnal variation of the needle, and, during this period, a number 

 of observations upon it have been made by others, but none of 

 them have led to any decided results respecting the general 

 nature and laws of the phenomenon. Two years ago, the Royal 

 Academy of Copenhagen proposed a prize question on the sub- 

 ject, which has not yet been claimed. 



It occurred to the author, that if he could reduce the action of 

 the terrestrial magnetism upon the needle, as mineralogists and 

 others had long been in the habit of doing, for the purpose of 

 detecting very small quantities of magnetism, the diurnal varia- 

 tion would then become more considerable. By pursuing this 

 idea, the most convenient method of executing which he found 

 to be the presenting of one pole of a magnet to the similar pole 

 of the needle, and the opposite pole of another magnet to the 

 opposite pole of the needle, he was enabled successively to. 

 increase the diurnal variation from a few minutes to 3*^ 40', then 



