20 BULLETIN 300, TJ. S. DEPARTMENT OF AGRICULTURE. 
machines. Although caterpillar tractors require no track, they have 
not given complete satisfaction when working under all the different 
conditions usually met with in operation. The wear on the chains 
is very great in sandy soil, and the expense of repairs and the time 
lost through breakdowns are likely to be considerable. 
VARIATIONS IN ROTARY TYPE. 
For the purpose of ehminating some of the weaknesses in the ordi- 
nary moving devices a novel design of walking scraper excavator of 
the rotary type has been put on the market. (See PL II.) Attached 
to the upper platform and extending through the machine in a direc- 
tion at right angles to that of the boom is a heavv steel shaft, on each 
end of which is a wheel segment. The shaft also carries a large gear 
wheel, which meshes with a pinion on the loading-dram shaft of the 
main engine. Suspended from the middle arm of each segment by 
means of a carrying beam and chains is a long shoe which affords a 
bearing for the segment as it rotates and propels the machine for- 
ward. The machine can be made to move in any desired direction 
by first swinging the upper platform. The excavator is moved 
ahead 8 feet during each complete revolution of the segment. The 
great advantage of this type of machine, as well as of the excavator 
mounted on caterpillar tractors, is the reduction in the necessary 
working force from four to two men, the trackmen being unnecessary. 
It is claimed that five men can take this type of machine down in a 
week and erect it in about two weeks. The machine weighs about 
60 tons and costs 87,000. Three cars are required for shipping it. 
Another form of the rotary type is the so-called boom-guided 
bucket excavator. The entire machine rests on two steel rails spaced 
12 feet apart and laid on short wooden ties. Either steam or gaso- 
line may be used as power. The unique feature of this machine is 
the boom on which the scraper bucket travels. (PI. Ill, fig. 1.) It is 
the purpose of this guide boom to overcome the difficulty of holding 
the ordinary bucket in place in passing from stiff to loose material. 
The bucket, which is a rectangular steel box open at the end 
toward the machine, travels upon the guide boom on steel rollers. 
To fill, the bucket is first pulled outward by the back-haul cable, 
which leads from the bucket to the head of the main boom and back 
to the engine. The guide boom is then lowered and the bucket pulled 
toward the machine. The bucket is dumped by being pulled up on 
the vertical end of the guide boom, the boom having first been swung 
around to the location at which the material is to be deposited. 
This machine is made with three different lengths of boom, a 30- 
foot adjustable boom which can be increased to 40 feet, a 40-foot, 
and a 65-foot boom. Buckets of 1J, 1J, and 2 cubic yards are used 
on these machines. It is claimed that 5 men can take down the 
