May 31, 1889.] 



SCIENCK 



415 



feet per second ; express-trains, 18.23 miles per hour, or 26.74 feet 

 per second. Allowing for station stops, the maximum speed will 

 be under 20.5 miles per hour, or 29.9 feet per second. 



The speed at which a cable for the transmission of power can be 

 run may be determined by the liability of the pulleys to burst under 



brakes are brought into action, and the pulling-power of the cable 

 gradually overcomes the inertia of the train. 



3. In answer to the third question it is sufficient to, state that the 

 length of the gripping-surface is 60 inches, which, used with a 

 cable of if inches diameter, and assuming only three-fourths of 



the action of centrifugal force, and this safe speed is determined by 

 Professor Unwin, for cast iron of 4,500 pounds per square inch 

 tensile strength, to be 215 feet per second ; so that, if we adopt 25 

 miles per hour as the desired velocity, which is nearly one-fourth 

 greater than now used, we shall have for our working speed 36.66 

 feet per second, or about one-sixth of the safe limit for cast-iron 

 pulleys. Hence there can be no question as to speed. 



2. To one familiar only with the cable grips at present in use, it 

 is but natural that this second question should cause considerable 

 apprehension, for there is not one which could be successfully 

 used for such velocity as has been above assumed. But the Rapid 

 Transit Cable Company have had this question of providing a grip- 

 ping-apparatus applicable for heavy trains and high velocity con- 

 stantly in view, and their experiments and labors have been largely 

 devoted to overcoming the difficulties encountered ; in fact, it may 

 be said to have been a sine qua noii, and they are at last prepared 

 to claim a successful solution of the problem. Their grip for such 

 service as is now under consideration is placed on a separate truck 

 or car, and hauls the train as a locomotive ; but instead of weigh- 

 ing 23! tons, concentrated as largely as possible on four driving- 

 wheels, it weighs less than 10 tons ; it is supplied with pumping- 

 cylinders to provide compressed air or vacuum for operating train- 

 brakes, and for moving itself about yards or switching from one 

 track to another. Curves of any radii which are practicable for 

 any other motive power are passed with equal facility, and the 

 cable can be picked up at any and all points on the line. It is ar- 

 ranged for duplicate cables, as is also the driving-machinery, so 

 that in case of any accident the idle cable may be picked up with- 

 out a delay exceeding five minutes, wherever the trains may be. 

 The gripping-device gives a very long contact, thus reducing the 

 unit pressure on the cable for a given weight of train. The grip- 

 ping surface is of leather ; and, to still further protect the parts in 

 contact from excessive wear, a very simple device sets the movable 

 gripping-parts into motion automatically before they are brought 

 into contact with the moving cable. Thus that which in all other 

 grips would be speedily cut out by the cable is in this case pre- 

 served, and little or no cutting can take place. When the parts 

 are moving at the cable speed, the pressure is applied, the grip- 



the periphery to be subjected to the gripping-pressure, will give an 

 available area of 246 square inches. The friction of leather on a 

 cable may safely be taken as 0.6 of the pressure applied, so that 

 for every pound of pressure there is 0.6 of a pound of pulling- 

 power. An elevated-railway locomotive with 37,400 pounds on 



drivers, may, under the most favorable conditions, exert from one- 

 third to one-fourth of this weight as tractive force, an average of 

 11,400 pounds, which this grip will produce with less than 78 pounds 

 per square inch, which may be multiplied several times without 

 injury to cable or grip. 

 4. Next as to the question of economy. In a cable system, 



