402 Chronicles of Science. [July, 



(that is, a solution of phosphorus in carbon disulphide) is placed on 

 the filter-paper ; the thread is cut and the balloon left to itself. In 

 the course of half a minute or so the explosion ensues. It is neces- 

 sary to have an excess of hydrogen in the mixture, because exosmose 

 takes place so rapidly that, by the time of ignition, the volume of 

 that gas is sensibly reduced. 



6. ENGINEEKING- CIVIL AND MECHANICAL. 



In our last number we gave, under the above heading, a brief ac- 

 count of narrow-gauge railways, which, during the period therein 

 referred to, had engaged considerable attention both in this country 

 and in Eussia. The necessity for improving the means of local 

 transit has, since then, continued to receive the consideration of all 

 most interested in the question; arid a " Tramways' Bill" has re- 

 cently passed through the Legislature, in which provision is made 

 for facilitating the construction and laying of tramways on common 

 roads. 



Street Tramways. — Tramways for passenger traffic have for some 

 time past been in operation in New York, Boston, Washington, New 

 Orleans, and they are becoming general in all the more important 

 towns of the United States. Paris, Genoa, Vienna, Copenhagen, and 

 Brussels, have all their tramways for passenger traffic, and they have 

 also, for some years, existed in Liverpool along the Dock sides. Some 

 years since iron rail tramways were introduced into London, but 

 after a short trial they w 7 ere ordered to be removed in consequence 

 of the obstructions they caused to ordinary vehicles. At the East 

 End of London a granite tramway has been in existence for many 

 years, extending from the western end of the Commercial Pioad East 

 to the West India Dock ; and in a circular by Mr. J. B. Piedman, 

 dated in March last, on the subject of Metropolitan Tramways, it is 

 stated that " practically the tramway is in as efficient working a state 

 as it was twenty years back." The late Mr. Walker conducted certain 

 experiments with granite tramways in 1829, which showed that a 

 powerful draught-horse could draw a load equal to 30 tons upon a 

 level, at the rate of four miles an hour ; and in his report on the 

 subject he said, " The friction is not more than upon the best con- 

 structed edge railways. I consider that the greater size of our 

 wheels, and there being no flange, compensates for the roughness of 

 the stones (from their being newly laid) as compared with an iron 

 railway." 



Whilst fully alive to the advantages of tramways for lessening 

 friction, attention has not yet been sufficiently given in this country 

 to the improvement of our macadamized roads by rolling ; and now 



