1863.] 



Trains passing through a Tunnel. 



83 



through the shafts ; but even had they been closed, it seems unquestionable 

 that the report, and of course the sound of a train, would travel through the 

 earth *. 



I should have prosecuted these researches further, especially in reference 

 to the velocity with which these tremors are propagated through the 

 ground, but that Lord Auckland's letter to me led me to hope that all 

 danger to the Royal Observatory was past, never to return. I therefore 

 contented myself with reducing the observations I had made. x\s, how- 

 ever, the Railway Moloch seems never likely to be satiated with victims, 

 and as the observatories of Oxford, Armagh, and again that of Greenwich 

 have been marked for sacrifice, it seems to me a duty to place before the 

 public the facts which had been collected at a great expense of labour, and 

 some pecuniary outlay. 



They were made without any bias, or any motive but a desire to ascertain 

 the actual truth ; and in addition to their bearing on practical astronomy, I 

 hope that they may not be without use in reference to some other depart- 

 ments of science. 



* An interesting fact was o'jserved with the maroons. They were fired vertically from 

 a mortar twenty feet from the observatory, and had fuses which gave them flight for six 

 seconds. The mercury showed the usual intense disturbance when the mortar was fired, 

 and also at the explosion of the maroons in the air. But there was also an intermediate 

 distur])ance which I cannot explain but by supposing it to be as it were an echo of the 

 earth-wave caused by the discharge of the mortar and reflected from the maiionry of the 

 tunnel. I showed it to the Marquis of Blandford, to Lord Alfred Churchill, and to Pro- 

 fessor James M^Cullagh ; unfortunately the nights Dr. Robinson and Mr. Warburton ac- 

 companied me to Watford, not a single star was visible. On repeating the experiments 

 at Campden Hill, nothing of the sort occurred. 



