902 



Popular Science Monihhj 



■^3^"^-^:'^ 



A passenger ferryboat rammed this mammoth floating drydock in a dense fog. The damaged sec- 

 tion promptly separated from the others, turned sidewise and floated inside its former companions 



Nothing Troubles This Drydock. 

 It Can Repair Even Itself 



THE big floating drydock in the harbor 

 of Tacoma, Washington, was rammed 

 in a dense fog by a passenger ferryboat, 

 and one of its four sections driven in. 

 The ferryboat was of the old-fash ned 

 river type with a draft of only three feet. 

 In the winds and currents of Tacoma's 

 open harbor it was notoriously unmanage- 

 able. 



But the drydock was a match for the 

 ferryboat. The section which the ferry- 

 bor.t had damaged was promptly sepa- 

 r»jl:ed from the others, turned sidewise, 

 and floated inside its former companions. 

 Men thereupon went to work with a will 

 and elevated the damaged brother above 

 the water's surface so that repairs could 

 be made. And by this time all four sec- 

 tions are back in the water again, joined 

 together, and doing each day their daily 

 work as if nothing at all had 

 happened. 



Incidentally it may be worth 

 while to note that do?toring up the 

 damaged section was the drydock's 

 first job, and it accord- 

 ingly started a life of 

 repairing by first re- 

 pairing itself. 



In the illustration 

 above, the entire dry- 

 dock is shown at thfe 

 left, while at the right 

 the damaged section is 

 shown inside the two submerged sections 

 of its former self, undergoing repairs. 

 The diagram below shows how collision 

 between drydock and ferryboat occurred. 



I 



Dry dock 



Ferry 



Pa^th 



Does a Locomotive Wheel Travel 

 Slower or Faster than the Train ? 



T is an interesting point to consider 

 that on a locomotive wheel, the cir- 

 cumference is continually traveling at 

 different speeds. First a point on the 

 circumference of the wheel will go faster 

 than the rest of the locomotive; then 

 that same point will go slower; at still 

 other times, the point will travel at a 

 speed equal to that of the locomotive 

 cabin. 



This paradox is explained by con- 

 sidering first the point on the circum- 

 ference farthest to the rear of the wheel's 

 center. When the center of the wheel 

 moves forward with the same speed as the 

 rest of the locomotive, that point will 

 move around and in a short time it will 

 get ahead of the center. Obviously, to 

 do this, this noint has to travel faster 

 than the locomotive. 



As the train moves 

 on from this position, 

 however, the average 

 speed of that same 

 point will become less 

 than that of the loco- 

 motive. This is evi- 

 dent, since the point 

 will soon change from 

 a position directly in 

 front of the wheel's 

 center to another point 

 directly in the rear. 

 This apparent para- 

 dox is not related to the old saw con- 

 cerning the relative speeds of a kangaroo's 

 hind legs and front legs when jumping 

 Australian sand hills. 



cvjrrervt forced 

 ferry agairvst 

 dry dock ' 



How ferryboat hit the" 

 dock that repaired itself 



