FARM EXPERIENCE WITH THE TRACTOR. 13 
However, the life of a tractor can not be properly expressed in years 
alone. The tractor is a machine; and, like all machines, its life 
depends on the amount of work it does and on the care taken of it. 
This life can be shortened by lack of proper care and by abuse in 
operation. The number of years a tractor will be available for work 
on a farm, therefore, depends only partly on the hours it will be 
required to work each year. But if the machine is given proper care, 
both when idle and when in use, the amount of work done per year 
will be the principal factor in determining its length of useful life. 
Table IV shows that during the working life of a tractor in ordinary 
farm service the amount of service obtained covers from 3,600 to 
11,000 working hours, including both traction and stationary work. 
From these figures it is apparent that a tractor might be worn out in 
less than two years if operated day and night continuously, while, 
on the other hand, if used only intermittently its life may be extended 
over a number of years, with proper protection from deteriorating 
influences when not in use. It might seem at first thought that a 
tractor could be made to last indefinitely by replacing worn-out parts 
with new ones, but there comes a time when the cost of such replace- 
ments becomes prohibitive and it is more economical to discard the 
old tractor and purchase a new one. The tractor's life is, then, the 
length of time it can be used before the repairs become so expensive 
as to make its further use uneconomical. 
While Table III showed the number of owners who believe the 
tractor to be a profitable investment, there were two related questions 
submitted to the owners which are not shown in the tabulations. 
These were "All things considered, is the tractor more satisfactory 
than horses?" and "Is it cheaper?" The answers received to these 
questions agree in many cases with those shown in Table III, but it is 
interesting to note that among the men who believed the tractor to be a 
good investment the number reporting the tractor to be cheaper than 
horses is greater than the number stating that it is more satisfactory 
than horses. On the other hand, among the men believing that the 
tractor is an unprofitable investment, the number stating that it is 
not cheaper than horses is less than the number stating that it is not 
as satisfactory. 
This would seem to indicate that among the successful owners the 
tractor's economy has been a greater factor than its general utility, 
while among the unsuccessful owners the expense has been a more 
important consideration than its unsatisfactory operation. 
FUELS USED. 
Table V shows the number of engines in each group which burn 
gasoline, kerosene, and motor spirits, respectively. From this 
table it will be seen that the percentage of kerosene tractors is slightly 
