1907-8.] On the Theory of the Leaking Microbarograph. 451 
The corresponding values of tss — p are then given by 
?/l = T( 
y 2 = 7(e^ T - l)e~^ ; 
fX 
y 3 = - 7(1 — ew(T+u-0 _ e ju,(T-«)_[_ e -^) • 
fX 
// = -7(1 -e-^ T )(l _ e -MT+xJ))ef*( 2 T+u-o 
IX 
(40). 
The broken curve OFGHK in fig. 8 shows the general form of the 
microbarogram in this case, the graph of rtf — Tt7 0 being ODECL. 
Microbarometric Observations at Loch Earn. 
In the autumn of 1905 a series of microbarometric observations were 
made with the object of throwing some light on the origin of the seiches in 
Loch Earn. Three Dines-Shaw instruments were placed at the vertices of 
the triangle, Killin (A), Lochearnhead (B), Ardtrostan (C). If we denote the 
sides and angles of this triangle by a, b, c; A, B, C, then roughly we have 
a = 5*60, 5 = 8-75, c = 6-10 (miles) 
A = 39°, B = 98°, C = 43°. 
The direction BC is about 4° north of east. 
In order to interpret a set of observations from three stations only, 
it is necessary to make some assumption regarding the wave - front 
or equiphasal line of the atmospheric disturbance. We shall take the 
simplest possible supposition, and assume the wave-front to be a straight 
line, and the propagation to be also rectilinear, and uniform with 
velocity Y. 
Then, if t x , t 2 , t 3 be the times of passage (say in minutes) of the same 
phase of a disturbance at A, B, and C, 6 the inclination (to northward) of 
the wave-front to BC, and <^> = 90 —0 the inclination of the direction of 
propagation (to southward) to BC, it will readily be seen that we have 
c sin (B - 0)/a sin 0 = {t 2 - t l )/(t 3 - 1 2 ) . 
This leads to 
cot 6 = { (t 3 - O cot B + (t 2 - t j) cot C )l(t 3 - t 2 ) ; 
and, since (p — 90° — 0, cot B = — 0T4, cot C = 1*07, we have the formula 
tan = { 107 (t 2 -y-0 ■ 14(* 8 - Q}/Cs - C) . 
(41). 
