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rOPULAR SCIENCE REVIEW. 
practically abolished, Mr. Bessemer has made an advance in principle on all 
previous attempts in this direction. Mr. Bessemer is having a vessel con- 
structed to test his plans. 
Rifled Gun. — A gun now in course of construction at Woolwich is ex- 
pected to prove the most powerful piece of ordnance ever produced. This 
is a 35- ton gun, carrying a projectile of 550 lbs. weight, propelled by a 
charge of 100 lbs. of powder. It is stated that this gun is expected to 
prove capable of penetrating a 15-inch plate, and judging from past expe- 
rience it ought to be pretty nearly competent to accomplish so much. How 
ships are to be built capable of resisting such a projectile, if indeed that is 
possible, is yet to be seen. 
Ventilation of Coal Mines.— Mechanical ventilation in coal mines i3 steadily 
gaining ground, on the older plan of producing a draught in the up-cast 
shaft by means of a furnace. Mr. D. P. Morrison recently read a paper on 
the subject before the North England Institute of Mining Engineers, at 
which he stated that in the deepest English coal mines, mechanical venti- 
lation would show an economy of 35 to 40 per cent, over furnace ventilation. 
After discussing various arrangements of mechanical ventilators, he gave 
the preference to the Guibal centrifugal fan. 
Steam Paviour. — In Paris, a steam paviour has been introduced to do the 
laborious work of the men with wooden rammers, whose appearance where- 
ever a street is being relaid will be familiar to our readers. The French 
machine is similar in principle to a steam hammer, and is moved about when 
at work by a horse. 
Ventilation in Railway Carriages. — Attempts are being made to secure 
more perfect ventilation in the carriages of the Metropolitan Railway, and 
to reduce the unpleasantly high temperature of the air. Experiments are 
being earned out on plans due to Dr. Croft, and are reported to have been 
successful, the anemometer showing a strong inflowing current, without any 
perceptible draught in the carriages. 
New Ventilating Machine. — M. F. Mulhausen, a civil engineer of Bruns- 
wick, is said to have invented a new freezing and ventilating machine. The 
cold is produced by the expansion of previously compressed air, a process 
which in principle was suggested originally, we believe, by Prof. James 
Thomson. 
Single Rail Tramway. — Mr. J. W. Addis, C.E., is experimenting in India 
on a new form of single rail tramway. The vehicles used in addition to the 
ordinary wheels have a pair of flanged wheels, one behind the other, run- 
ning on the single rail, which is laid at the centre of the track. The 
flanged wheels are adjusted by a screw so as to take all the weight off the 
ordinary wheels, without lifting them much above the roadway. An expe- 
rimental line lias been laid, in part at an incline of 1 in 40, and along this 
a pair of bullocks draw a load of 3 tons. The advantages claimed for the 
system are — first, a very great diminution of power expended in hauling as 
compared with traction on common roads ; secondly, that the cost of construc- 
tion is only one-half that of an ordinary tramway with two lines of rails. 
A tramway or railway on a similar principle was, we believe, tried some 
time ago in France. 
Rock Boring. — AVe learn from a letter in the Engineer , that the diamond 
