1 Ocr.,1901.] QUEENSLAND AGRICULTURAL JOURNAL. 429 
It does not come within the scope of the present article to explain the 
principle on which this instrument is constructed, nor to discuss the many uses 
to which it can be put. Volumes have been written on the subject, and by 
abler pens. It is sufficient to state that the rule is simply the mechanical 
application of the principle of logarithms. 
Asa rule, the yield of grain for each separate plot is weighed in lb., 
and from this the yield per acre in standard bushels is calculated. As in most 
cases the plots are of the same size, it is only necessary to first set the slide 
rule at the constant number, or divisor, and then opposite to each weight per 
plot will be found the yield in bushels per acre, so that the results for a large 
number of plots can be read off at one operation. Where the plots vary in 
size, the area in square links or square feet must be ascertained, and, settin 
this at the proper divisor, opposite the lb. per block, will be found the bushels 
per acre. As experimental plots are now usually sown in drill widths, so 
knowing the width of the drill, by setting the length of the plot to the ascer- 
tained divisor, the yield per acre in bushels will be found opposite to the 
weighed yield in lb. per plot. The following table gives the divisors for the 
conditions mentioned above :— 
Dimensions. Yield Answer. Wheat. Oats. Barley. 
Length in feet ...|lb. per plot |lb. per acre | 43,560 43,560 43,560 
” - ” ” tons —,, 19°44 19°44 19°44 
Ten? % Desai #8 4 7) bushels ,, 726 1,089 871°2 
ength in feet and drill | ! 4 
Width, 8 feet (or rows) J yo» 93 | 90°75 116,125 108°9 
Length in links Ss; 3 +) Ib. per acre |100,000 —_|100,000 100,000 
meyers sat errand | AE tm te tons ,, 44°64 44°64 44°64 
atl 4 _ a aah a 5 n bushels ,, 1,666°6 | 2,500 2,000 
ength in links and dri 7 «| oR 
Width, 8 feet (12 rows) } cd ” ” 2? 9 187°5 20625 165 
General rule for finding a divisor:—(1) When the area of the plot is 
known, divide square links or square feet to the acre by the number of lb. to 
the bushel or ton. (2) When the plots are in drill-widths, divide the square 
links or square feet to the acre by the number of Ib. to the bushel or ton, and 
by the width of the plot in links or feet. 
This work is best explained by examples, and below will be found the 
working of a set of examples taken from the College experimental yields. 
It must be noticed, first of all, that the A and B lines of the slide-rule 
only are used, and to ensure that the correct number of tens will be allotted to 
the answer, it will be well to give the rule for slide-rule numeration. The 
lines are divided into two sections, and, to prevent confusion, only one section 
of the A line should be used. In this case, if the numbers are both on the 
_ same section of the B line, the difference of the whole numbers on the A line 
is the same as the difference of the whole numbers on the B line. If the 
numbers are on different sections of the B line difference of A integers 
equals difference of B integers plus 1, if answer on right-hand section; mimus 
lif answer on left-hand section. 
Examples. 
1. A plot contains 13,500 square feet, and the yield is 454 lb. wheat. 
How many Ib. per acre are there? 
Set 13,500 on B to 43,560 on A, and opposite 454 Ib. on B. 
answer—1,465 lb. on B. 
Find the 
A 48,560 1,465 
B_ 18,500 454 
2. With the same area and yield, how many bushels tofthe acre ? 
Set 18,500 on B, to 726 A, and opposite 454 on B find bushel per acre. 
A 726 24:4: bushels 
B 13,500 454 
le 
