630 [June 18, 



magnetic force when the sun is south than when he is north of the 

 equator. 



The author concludes this section of his investigations by drawing 

 the attention of the Royal Society to this concurrent evidence, from 

 the observations of three observatories situated in parts of the globe 

 so distant from each other, of a semiannual inequality having such 

 strong features of resemblance in both hemispheres, and remarks 

 that it seems difficult to assign such effects to any other than to a 

 cosmical cause. The "inequalities" may in themselves seem to be 

 small ; but judged of scientifically, i. e. in the proportions they bear 

 to their respective probable errors, they are large. 



IV. "Experiments, made at Watford, on the Vibrations occa- 

 sioned by Railway Trains "passing through a Tunnel." 

 By Sir JAMES SOUTH, LL.D., F.R.S., Member of the 

 Board of Visitors of the Royal Observatory, Greenwich. 

 Received June 17, 1863. 



(Abstract.) 



These experiments were made in consequence of an attempt in 

 1846 to run a line of railway through Greenwich Park, in what 

 seemed to several competent judges a dangerous proximity to the 

 Royal Observatory. 



It was abandoned, but (as Sir James South was informed) only 

 for a time ; and he thought it right to make some examination of 

 the probable effects of such a vicinity, especially as to the power of 

 a tunnel in deadening the vibrations. 



The Watford tunnel was chosen as the observing station, being, 

 on the high authority of the late Mr. Warburton, in ground very 

 analogous to that on which the Royal Observatory stands ; and every 

 facility for making observations was afforded by the late Earl of 

 Essex, through whose park and preserves this tunnel passes. 



As the chief inconvenience to be feared from the proposed railway 

 was the disturbance of the observations by reflexion in mercury, it 

 seemed best to take a series of these under circumstances as nearly 

 as possible resembling those which might be expected at Greenwich. 

 An Observatory was therefore erected, in which a large and powerful 



