1900.] 



on the Great Alpine Tunnels. 



431 



the main line between Florence and Bologna, through the Apennines. 

 This is a railway of single line, and was built many years ago by 

 the late Mr. Brassey. There are 52 tunnels in all, but those on the 

 eastern side are of comparatively little importance. On the western 

 slope the gradient nearly throughout is 25 per thousand (or 1 in 40), 

 and it is here the greatest difficulty exists. There are several tunnels 

 whose lengths approximate to 1000, 2000, and 3000 yards, and the 

 traffic is both heavy and frequent, the locomotives very powerful, 

 with eight wheels coupled. 



Under any conditions of wind the state of the longest tunnel is 

 bad, but when the wind is blowing in at the lower end at the same 

 time that a heavy goods or passenger train is ascending the gradient, 

 a state of affairs is produced which is almost insupportable, and one 

 might as conveniently travel in a furnace flue. 



PLAN. 



Fig. 6. — The Saccardo System of Ventilating Tunnels. 



A heavy train of dining and sleeping carriages, with two engines, 

 conveying one of the crowned heads of Europe and suite, arrived at 

 the exit of Pracchia tunnel with both engine-men and both firemen 

 insensible : and in other cases passengers have been seriously affected. 



Owing to the height of the mountain no shafts are available ; but 

 Signor Saccardo places a ventilating fan near the mouth of the 

 tunnel, and blows air into it through the annular space which exists 



