WEIGHT AND MATERIAL. 



It may be placed upon wheels and obliged to 

 follow the inside of a circular path, as in the 

 case of a bicycle or small car which is used 

 for the performance called looping the loop 

 (see Plate III.). The necessary speed is ob- 

 tained by running previously down a steep 

 descent somewhat higher than the circle to 

 be traversed ; and this is sufficient to carry 

 the car or bicycle right round a track on the 

 inside of a vertical circle, the passengers or 

 rider crossing over at the top with their heads 

 down and their feet up, held up by centrifugal 

 force against their inverted seats, and in perfect 

 safety so long as the mechanical arrangements 

 are all flawless and the cyclist retains his nerve. 



So far as this performance is a demonstra- 

 tion of scientific truth, its purpose would be 

 equally well served by having dummy riders, 

 but perhaps its fc drawing " power would be less. 



Advantage is taken of this centrifugal force 

 to separate more quickly things which separate 

 slowly by weight. Such means are employed 

 for the separation of crystals and precipitates 

 from their solutions ; of water from washed 

 linen, again because it is heavier ; and of cream 

 from the watery part of milk, because it is 

 lighter. But where the difference of weight is 

 not great, the process of separation is slow. 

 If a pint of cream weighs eighteen ounces, while 

 the same volume of water weighs twenty, the 

 difference, two ounces, is the floating power 



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