.s/A' WILLIAM SIEMENS, F.R.S. 353 



apparent sluggishness of the air to expand throughout its 

 course, by the fact that the medium was not pure air, but air 

 mixed \vith vapour of water, which mixture would follow another 

 law of expansion than that of either fluid taken separately. He 

 dissented entirely from that view of the case. He had shown, 

 ami Professor Unwin had quite confirmed that view, that the air 

 expanded isothermally that both air and vapour would pass 

 through a tube without altering in temperature ; therefore no 

 condensation of the vapour would take place ; and as vapour and 

 air both followed the law of Mariotte in precisely the same 

 manner, there could be no difference whether dry air was used or 

 air containing a slight proportion of vapour. 



In advocating the use of the radial system in preference to 

 the continuous or circuit system, Mr. Preece said that he had 

 travelled over the continent of Europe with a view of ascer- 

 taining the working of those systems elsewhere ; and that, while 

 he found the radial system established in Brussels, he ascertained 

 that at Berlin the circuit system, which had been adopted in ls<;;5, 

 had failed. This was startling news to him ; because, although 

 he had never described the system as established at Berlin, he had 

 referred to it, and his brother also had referred to it, in his paper, 

 as an historical step towards the accomplishment of the circuit 

 or continuous system as established by them in London. He 

 accordingly wrote to Berlin for information, and he had ascer- 

 tained that, so far from the system having failed there, it had 

 been during the last twelve years in uninterrupted operation, and 

 that the only thing that could be construed into a partial failure 

 was the circumstance that after the one circuit from the telegraph 

 office to the Bourse had been established, a second circuit from 

 the telegraph office to the Brandenburg Thor was added, and 

 it had been found that the boiler power was not sufficient to work 

 both systems continuously together. For a time, therefore, and 

 probably at the very time when Mr. Preece paid his visit to 

 Berlin, the one system was shut off when the other was worked 

 between the telegraph station and the Exchange during the busy 

 part of the day. With that exception, which he uudei stood had 

 since been set right by the addition of boiler power, the system 

 had been working precisely in the same manner as it had been 

 established twelve years ago, and it had given no cause of 



VOL. II. A A 



