130 Prof. Challis on the Eccentricity of the Moon's Orbit. 



8. Carbonic Acid in Water. 



This gas was prepared by the action of strong sulphuric acid 

 upon chalk, a few drops of water being added to the mixture. 

 The gas, thus steadily evolving, was washed by being passed 

 through boiled water. The experiment gave, — 



The three conditional equations from the mean 1, 2, 3, 4 and 

 2, 3, 4 and 3, 4, 5, 6, give the interpolation formula, 



c =1-7967 -0-07761* + 0-0016424 1*, (25) 



and from this the following coefficients are found : — 



[To be continued.] 



XVI. On the Eccentricity of the Moon's Orbit. 

 By Professor Challis*. 



IT is a satisfactory result of the discussion relating to the 

 moon's orbit which has recently appeared in this Magazine, 

 that it has drawn attention to the general question of apsidal 

 motion, which is one that is by no means exhausted. In the 

 Number for last January, Mr. Thacker has solved a problem of 

 this class by a method which shows the advantage of employing 

 for the purpose the first integrals of the differential equations of 

 the motion. I have used an analogous method to determine 

 the motion of the apses of the moon's orbit. In the problem 

 above mentioned, the force is supposed to be wholly central, and 



to be expressed by the function ~ + fi'r, and the solution leads 



* Communicated by tbe Author. 



