1863.] 623 



or oxygen. The gases named have the same specific heat for equal 

 volumes ; but a hot object placed in hydrogen is really touched 3'8 

 times more frequently than it would be if placed in air, and 4 times 

 more frequently than it would be if placed in an atmosphere of oxygen 

 gas. Dalton had already ascribed this peculiarity of hydrogen to the 

 high " mobility" of that gas. The same molecular property of hy- 

 drogen recommends the application of that gas in the air-engine, 

 where the object is to alternately heat and cool a confined volume of 

 gas with rapidity. 



II. " Results of the Magnetic Observations at the Kew Obser- 

 vatory, from 1858 to 3862 inclusive." No. I. By Major- 

 General EDWARD SABINE, P.R.S. Received May 21, 1863. 



(Abstract.) 



The first three sections of this paper are occupied by a discussion 

 of the Laws of the Disturbances of the Magnetic Declination at Kew, 

 derived from the photographic records of the Kew Observatory be- 

 tween January 1, 1858, and December 31, 1862. In the first sec- 

 tion a synoptical table is given, showing the direction and amount of 

 the easterly and of the westerly deflections of the declination magnet 

 at 24 equidistant epochs on each of 95 days of principal disturbance 

 occurring in the years 1858 to 1862 inclusive. The deflections are 

 measured from the normals of the same month and hour, computed 

 from the undisturbed positions at the same epochs on the 1825 days 

 comprised in the five years since the commencement of the photo- 

 graphic records. The phenomenal laws of the disturbances on the 

 95 days are then investigated, and are compared with the correspond- 

 ing laws derived from a far larger number of observations in the 

 same years, taken out by the well-known process employed by the 

 author in the reduction of the observations of the colonial magnetic 

 observatories. The result is shown to be that, so far as the laws of 

 the disturbances are concerned, the two processes furnish mutual 

 confirmation the laws being approximately the same whether they 

 are derived from the whole body of the hourly positions, or from 

 that portion only which includes 95 days (or on an average 19 days 

 in each year) which were specially affected by disturbance, but that, 

 for the purpose of eliminating the effects of the disturbances in the 



