160
��Popular Science Monthly
��to two other larger sprockets, one bolted to each of the rear wheels of the truck. The motor power is thus transmitted to the jackshaft, to
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��the jackshaft sprockets and thence through the chains to the rear wheel sprockets.
The internal-gear drive method shown in No. 4 also employs a jackshaft but this, instead of being mounted on the truck frame, is made into a unit with a stationary axle carrying the rear wheels. The wheels are revolved through small pinions positioned on the ends of the jackshaft which mesh with large internal gears bolted to the rear wheel spokes.
The bevel drive is used mostly on trucks of one-ton capacity and under. It is not used on larger trucks because ;,— - .
the greater gear reduc- tion necessary due to the greater weight of the truck and its load would make the bevel- pinion too small or the bevel - wheel too large for practical purposes. This neces- sarily larger gear re- duction is secured by means of the tloublc- chain dri\e b>' making the driving-wheel sprockets much larger than those on the jackshaft.
On the other hand, the necessary gear reduction for larger than one-ton trucks can be secured by means of the worm and worm- wheel due to the design of the worm- teeth and its rubbing instead of roll- ing action on the worm-wheel. It is also more efficient than the bevel or double-chain methods and delivers more power to the rear wheels becauso of llu- elimination of much of the friction of the
��bevel-pinions and chains. It also has the advantage o\'er the double-chain method in being an enclosed dri\-e, like the in- ternal-gear type,
���Fig. 3. Double-chain drive. The motor-shaft
ends in a jaclcshaft which transmits the power
to sprockets cormected by chains
���Fig. 4. Internal-gear drive. A jackshaft
pinions with two large meshed wheels on
the back axle
��thus preventing dirt and grit getting on to the driving members, and causing loss of power and excessive wear.
Another advan- tage of the worm drive over both the chain and internal- gear types is that the aggregate parts weigh less than either. This light- ens the truck, permitting more of the motor power to be used for hauling the load to be carried instead of moving the heaN'j' \'ehicle itself.
Measuring Rainfall on the Farm
AN excellent equipment for collecting and meas- uring either rain or snow consists of a simple pail or bucket. The location selected for setting out the pail should be in some open lot or field un- obstructed by large trees or buildings. If the diameter of the pail is just 10}^ ins. at the upper edge, each ounce of water collec- ted represents 0.02 in. of rainfall. The pail should hold twelve quarts, in fact, most twel\e-(iuart pails are exactU- io32 '-is. at their ui)per edge. The depth of the rainfall, as shown by the water caught, may be found by w^eighing the contents of the pail. An ordinary small balance which reads in ounces and half-ounces is suitable for the purpose. In hot weather, when water ex-aporatos quickly, the rec- ord should be made as soon as the rain has stoi)ped, if possililc.
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