Page:Popular Science Monthly Volume 91.djvu/47

 Popular Science Monthly

��balanced. They begin to revolve on their pins, toward the low-pressure side. The high-pressure side of them no longer carries its wheelshaft pinion around unyieldingly. It lags till pressures are equalized, the wheelshaft with the higher resistance turn- ing more slowly and the other wheelshaft more rapidly in the same proportion. The total of power utilized remains unchanged, except that a portion of it is spent in over- coming the friction of the revolving pinions.

As friction adds tooth pressure on both sides, it may be purposely increased

���Links and

eccentric5 An eccentric can drive a link in and out but cannot be rotated by- turning the link around

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��turned on. Suppose, further, that one wheelshaft resists very little and does not equalize tooth pressures until it is revolved eight times as fast as the other. Then the differential works four times as much as before and the value of the friction rises rapidly, perhaps from 2 to 8. The power is consumed. By arranging the friction on a less drastic scale, however, one can have a shaft which offers a rather small resistance under small differential action, yet equals the resistance of the other shaft as soon as its rotary velocity becomes only two or three times as high, after which no greater difference in shaft speed can be pro- duced. The power is then divided somewhat on this plan: 2 for the slow shaft, 1 for the small friction identified with its side of the dif- ferential action, 4 for the friction of the rapid shaft and I for driving it. If the wheel of the rapid shaft has no trac-

��It is built strong enough to resist the stresses that arise in its operation

��tion, there is still a net power of 2 for driving.

��to modify the action of the differential. For example, if the power delivered to the casing has a numerical value of 8 and the resistance of each shaft against rotation at a certain velocity is 4, no friction in the differential arises. But when road contact interferes and one of the shafts produces in- creased resistance at this velocity but only 4 at a velocity 33^ per cent higher, while the other shaft produces 4 at a velocity 33^ per cent lower, such as may be the case when a vehicle is made to turn or a fairly sharp curve, one shaft is turned twice as fast as the other and a certain friction is produced. In the ordinary differential this friction i negligible; but suppose it i made to have a value of 2 then there is only a power of 6 available and there is less than 4 for each wheelshaft. The < vehicle speed is reduced or more power must be

��A L

���The refrigerator-basket is the picnic party's ice-box. In it all perishable food is preserved

��A Refrigerator Basket for the Picnic Outing

LL the luxuries of home are now at the disposal of the vacationist starting off for a picnic at the beach or in the woods. The increasing vogue of automo- bile touring trips has also created a demand for portable creature comforts. A refriger- ator basket is a refrigerator in minia- ture, which keeps the butter hard, the meat fresh and the milk sweet. It consists of a rust-proof metal food container with a smaller ice compartment partitioned off at one end. Around this shell is a layer of insulating material to keep the cold air in and the warm air out. Externally the carrier is a reed basket with convenient handles and straps to bind the lids down. Separate lids are provided for the two compartments.

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