HOURLY OBSERVATIONS OP AIR TEMPERATURE AND PRESSURE. 
619 
Value of T . . . . | 
P + ; <2 + • 
p- , q ^ . 
F- , <2 - > 
p + , q- . 
X 
0 to 90° 
360° - 
270° to 360° 
180° + X 
180° to 270° 
180° — X 
90° to 180° 
Value of /tj ... 1 
90“ - Tj 
90° - 
450° - T] 
90° + X 
450° - Tj 
270° - a; 
450° - T] 
270° 4- a; 
Value of /(o . . . 1 
. 4.5° - iTo 
45° - i'B 
225° - IT3 
45° + pv 
225° - iTo 
135° - 
225° - iTo 
135° + la; 
Value of yiig . . . 1 
30° - iTg 
30° - 
150° - XX 
30° + lx 
150° - iTg 
90° - xx 
150° - 1T3 
90° + xx 
Value of ... 1 
22V - fT, 
22|° - fa; 
1121° _ iT, 
224° + ix 
1121° - iT^ 
671° - ir 
1121° _ iTj 
671° + 
The values of P aucl jx were throughout obtained from the calculated values of jo, q, 
by means of a slide rule arranged for the solution of the equations, tan x = p/q, and 
P = y)/sin X, as shown below :— 
Fixed Rule. 
Slide. 
The upper scale of the Jixed rule is graduated to show logarithms of numbers, and 
serves to indicate the value of log p. The graduations of the lower scale of the 
same rule represent log tangents to radius equal 1 on the upper scale and indicate 
log tan X. 
The graduations of the lower edge of the slide rule are logarithms of numbers in 
the reverse order to those of the fixed rule, and indicate the values of log q. The 
upper edge of the slide rule is graduated to show log sines to the same radius as 
before, and indicates the value of log sin x. 
The rule is used as follows :—The slide is moved in the groove till the zero point A, 
on its top edge, comes opposite to the graduation corresponding to log p) on the fixed 
rule. Then opposite the graduation corresponding to log q on the lower edge of 
the slide will be found, on the scale of log tangents, the value of the angle x, or 
log tan X log p) — log q. 
4 K 2 
