312 Stonry— Of Atmospheres upon Planets and Satellites. 
escape from B when B is at rest. If B rotates, a less velocity relatively to the 
surface of B will suffice, provided that the missile is shot off in the direction 
towards which the station from which it starts was being carried by the rotation 
at the instant of projection. 
Cuarter IV.—Of the Earth. 
Let us apply these elementary dynamical considerations to the Earth. In 
doing this, we may assume— 
RF (the Earth’s equatorial radius), : 6378 kilometres. 
h (the height of the atmosphere), : = = 200m: 
g (gravity at Z, a station on the equator, at 
the bottom of the atmosphere), 
w (the velocity at the equator due to the 
Earth’s rotation), . ‘ ; : . = 464 m./sec. 
978-1 em. / sec. / sec. 
We shall need one other datum, viz. the highest temperature which can be 
reached by the air at station Z’, where LZ’ is a station at the top of the atmo- 
sphere, over the equator. To enable us to arrive at definite results, we shall 
regard this temperature as — 66°C. Our numerical results would be affected, but 
would only suffer a slight alteration, by substituting for this particular temperature 
any other which is admissible. It is, accordingly, legitimate to make our compu- 
tation on this assumption, viz. that the temperature at Station EZ’ is 66° C. below 
freezing point. At this temperature Clausius’s formula, equation 1, gives for 
the velocity of least square in a gas 
D= (asta) |, 
P 
= 1603/ Jp, (9) 
if we here use w to signify the velocity of least square at this particular 
temperature. 
Let us next calculate a, the acceleration due to the attraction of the Earth at 
Station H# (on the equator, and at the bottom of the atmosphere). Here 
@= 9+ (6) 
where g is gravity at the equator, and y the acceleration due to the Earth’s 
rotation, @e. 
w _ (46411) 
VS pe Tearenn 
= 3°4 cm. /sec. / see., (7) 
