318 Introduction to the Study of Science 



and steam power practically discontinued on these sections. 

 Hundreds of miles additional are well along in construction, 

 and still more are planned. 



An example of electrification of steam railroads is that 

 of the Chicago, Milwaukee, and St. Paul. Four engine di- 

 visions comprising 440 miles of road and 160 miles of spurs, 

 sidings, and yards are electrically operated. The stretch of road 

 (see table, page 273) crosses three mountain ranges (Fig. 98) : in 

 Big Belt Mountains at an elevation of 5788 feet ; the Rockies at 

 a maximum elevation of 6322 feet, this relatively low elevation 

 for the Continental Divide being due to a tunnel half a mile 

 long ; and the Bitter Root Mountains at an altitude of 4163 

 feet through a tunnel nearly 9000 feet long. The east approach to 

 the Rockies (Fig. 98) has 20 miles of road with 2 per cent grade. 

 The west approach to the Big Belt Mountains has 40 miles of 

 1 per cent grade, a long, heavy pull for steam locomotives. 



It is probable that the rest of the road to the Pacific coast 

 will be electrified, aggregating a total distance of 850 miles. 

 The Cascade range of mountains is crossed at an altitude of 

 3010 feet by a grade that is very light. 



141. The electric locomotive. The electric locomotive 

 (Fig. 99) is 112 feet and 8 inches in length and weighs about 

 284 tons. The estimated weight upon the driving wheels is 

 200 tons. The locomotive is rated at 3000 horse power for 

 continuous operation, and 3440 for one hour. The motors 

 are flexible or like a good horse which under stress may exert 

 additional power to haul a limit load over a steeper grade. 

 The tractive effort or pull available for starting a load is about 

 120,000 pounds, but for continuous pulling is about 85,000 

 pounds. A freight locomotive can haul a 2500-ton train on 

 all gradients up to and including one per cent, at a speed of 

 16 miles per hour ; or a load of 1250 tons on gradients up to 

 and including two per cent, the maximum gradient on the road, 

 at the same speed. For example, one locomotive hauls a train 

 of the larger load until it arrives at a grade steeper than one per 



