421 



circuits, and thus the bells at the respective stations are actuated by 

 the batteries of the respective stations. If ten blows with a pause of 

 a minute, and then ten more, is the signal that the engine is disabled ; 

 ten blows, and a minute of contact, that an accident has happened ; a 

 ringing continued beyond ten, that the permanent way is obstructed, 

 the stations at either side are advised and can take the measures 

 necessary to meet the case. 



These contacts may be made by hooking a wire or rod on to the line 

 wire and making the necessary contacts with the rail ; or, which is 

 better, by establishing contact-makers, properly secured at frequent 

 intervals on the telegraph posts. 



This system gives to those in charge of disabled trains a certain 

 means of asking for assistance from any point of the open railway, 

 without any training beyond that of counting ten slowly and cor- 

 rectly. In practice, as between Red-Hill and Reigate, no inconveni- 

 ence or loss of electricity has been suifered from counterbalancing the 

 two currents. 



The author states that there are other properties of opposed 

 currents to be communicated on another occasion. 



II. " On the Action of Aqueous Vapour in disturbing the Atmo- 

 sphere." By THOMAS HOPKINS, Esq. Communicated by 

 W. FAIRBAIRN, Esq., F.R.S. Received January 2, 1857. 

 (Abstract.) 



In this paper it was maintained that the great disturber of the 

 equilibrium of atmospheric pressure is the aqueous vapour which is 

 diffused through the gases. These gases, when ascending, cool (say 

 5) through expansion by diminution of incumbent pressure, whilst 

 the vapour that is within them cools only 1 ; and a consequence is, 

 that when a mixed mass ascends, the vapour is condensed by the 

 cold of the gases. It is well known that condensation of vapour 

 gives out much heat, and this heat warms and expands the gases 

 when they are forced to ascend, taking vapour with them ; and the 

 process being repeated and continued, an ascending current is pro- 

 duced in the atmosphere, cloud is formed, the barometer sinks, rain 

 falls, and winds blow towards the part. 



This was shown to take place in all latitudes, producing disturb- 



