50 On Aerial Navigaiton. 
In the second paragraph, respecting lateral motion, it is ob~ 
served that the tacking plan, though worthy of much considera- 
tion, is incapable of counteracting any considerable wind, “ asa 
little calculation will show.’ I must here remark, that if your 
correspondent will honour with his attention my statement 
respecting a Montgolfian balloon constructed on the tacking 
plan, in your Magazine for March 1816, and will recalculate 
the powers of that construction, he will find that the horizontal 
speed will be about twenty miles per hour in calm air; but he 
must not, as he proposes, consider the major axis as elevated in 
an angle of 45° with the horizon; but at an angle of 30°, which 
will be found to cause the path of the machine to be in the for- 
mer angle; 15° or 16° being lost, in what is similar to lee-way 
in ships, according to the flatness of the top surface of the bal- 
loon. Although a velocity of twenty miles per hour will not 
overcome some winds, and would scarcely be at par with what 
Mr. Smeaton calls ‘very brisk’’ in his table; yet it would over- 
come what he terms “gently pleasant,” at a speed of sixteen 
miles per hour ; and what he terms “ pleasant brisk,” at about 
seven and a half. Very few days in the year have what is thus 
called very brisk wind, and it is even in this case 32 to | that it 
does not blow from that point of the compass which is the pro- 
posed direction of steerage. In most oblique cases the power of 
the machine will give a great command of diagonal steerage 
within the semicircle opposed to the wind ; on either side it will 
be no impediment ; and in the whole semicircle behind the wind 
it will add to the velocity required. Hence, as on most occa- 
sions a choice of time is left, winds will be of infinite use in 
aérial navigation, even should twenty miles per hour, in calm air, 
prove to be the limit to the velocity of these machines. The 
difference of the currents in the upper and lower strata of the 
atmosphere, it is well observed by your correspondent, will lend 
great assistance to the steerage of balloons, as will also the sin- 
gular fact of their following the direction of rivers, which is pro- 
bably an electric phenomenon, rivers acting like discharging 
rods by connecting the opposite electrical states of distant re- 
gions of the atmosphere, as is exemplified by the greater frequency 
of accidents from lightning on their banks than in ordinary si- 
tuations. 
In the third paragraph your correspondent states the failure 
of oars in moving balloons to have arisen from their being ap- 
plied to the car, in lieu of “ their line of pressure passing through 
the centre of pressure of the whole system,” much of the power 
being thus applied towards communicating a rotary movement 
of the car round the balloon. J do not conceive this to be the 
cause 
