NATURE 
365 
who has had thirty years of observation in this direction, 
says :— 
: CAL the observations that have been made in the 
motions of the atmosphere, as well as the deductions from 
theoretical considerations, lead to the conclusion that the 
resultant motion of the air around the whole earth, within 
the temperate zones, especially about the middle of them, 
is from west to east. Prof. Watson, the distinguished 
astronomer of the Michigan University, writes, ‘1 beg to 
say that there ought to be a strong current of air moving 
eastward in the upper regions, and that the experience of 
aéronauts goes to show that what the theory predicts 
actually exists. It seems to me quite possible to make 
an aérial voyage to Europe, and with great rapidity.’ 
William H. Wahl, secretary of the Franklin Institute at 
Philadelphia, writes, ‘I believe that, generally, Prof. 
Wise’s proposition, concerning the existence of the ele- 
' vated easterly current, is correct, and the same view is 
entertained upon theoretical grounds by meteorologists.’ 
To the same effect writes Prof. Brocklesby, of Trinity 
College, author of ‘Elements of Meteorology,’ a work 
recognised as the best elementary text-book on the 
subject.” 
Still Prof. Henry is by no means enthusiastically in 
favour of seeing the dangerous voyage undertaken ; he 
speaks of it as at the best extremely hazardous, and 
would prefer that some one else in whom he is less in- 
terested than he is in Prof. Wise would undertake the 
risk. His letter to Mr. Wise, in which he thus speaks, 
is worth quoting for its meteorological value. He says— 
“T have no doubt of the fact that, if your balloon can 
be sustained in the air sufficiently long, a voyage might 
be made across the Atlantic ; but this is the point which, 
it would appear to me, from my partial knowledge of 
what has been accomplished in the art of ballooning, is 
yet to be satisfactorily established. No one, however, 
has had more experience in the art than yourself, and you 
ought not to venture on the hazardous voyage without the 
fullest assurance that the balloon can be sustained at the 
requisite elevation for, say, ten days. 
““T think it probable that over the ocean at a consider- 
able elevation, the tendency to meet adverse currents will 
be less than over the land ; on the other hand, however, 
there will be a chance of meeting a cyclone, which might 
carry you around a circle of several thousand miles, and 
throw you back over the coast of the United States, since 
you would be most likely to meet the northern portion of 
-the great whirl, which would be moving in the western 
direction, the only possible escape from which would be 
by ascending to a very high elevation. The higher tem- 
perature of the Gulf Stream tends to produce an ascent 
of air above it during the colder months of the year, but 
in summer this effect would scarcely be perceptible. 
“Your remark in regard to the greater velocity of the 
easterly motion of the balloon at night is in accordance 
with meteorological principles, since at this period the 
unequal heating of the earth by the direct rays of the sun 
does not take place, and hence adverse currents are not 
as frequent. The cooling of the atmosphere in that part 
of the earth which is in the shadow will tend to produce 
at the surface of the earth, after sunset, a westerly current, 
while at a certain elevation above the earth, the current 
would at the same time be in an opposite direction. In 
the morning, just before and after sunrise, the current at 
the surface of the earth, produced by the cooling, would 
be eastward, while that in the atmosphere above would 
be westward.” 
There can beno doubt that this daring expedition, 
whether it descends without mishap on the shores of 
Europe, or comes to grief in the middle of the Atlantic, 
will add something to our knowledge of the atmosphere ; 
but many will no doubt think that all the knowledge that 
will be acquired by this sensational and hazardous 
method might be acquired by safer and more ordinary 
methods. We certainly, with all our heart, wish the 
enterprise complete success; but we think it very 
pertinent to refer to some remarks on the project in Le 
Nature by the experienced balloonist, M. G. Tissandier, 
After referring to the theory of the easterly current in the 
atmosphere, M. Tissandier says, “We leave to the 
aéronaut all the responsibility of this hypothesis, which 
appears to us to be based upon vague conjectures ; we 
should have a little more confidence in the resources 
which he expects to find above the Gulf Stream. This 
warm river, which traverses the extent of the Atlantic, 
should draw along with it a current of air, which the 
aérial navigator might take advantage of. 
“We do not doubt the good faith of the aéronaut, who 
has already proved himself to be possessed of boldness 
and courage, but we believe he has not maturely con- 
sidered the problem he proposes to solve. Togo from 
New York to England, the aéronaut must travel a space 
of about 5,500 kilometres. Suppose that exceptional good 
fortune favours him, that a favourable wind, of mean 
intensity, having a speed of ten metres per second, blew 
regularly from west to east, without deviation, he must 
necessarily sojourn in the atmosphere six or seven days at 
the least, since the distance traversed in twenty-four hours 
will be, according to our hypothesis, 864 kilometres. But 
can an aérostat, no matter how voluminous it may be, 
constructed under existing conditions, and notwithstand- 
ing its complete impermeability, remain in the atmosphere 
for seven days? To this we reply, with the utmost confi- 
dence, in the negative. In fact, when a balloon quits the 
earth, as it rises a part of the enclosed gas is at once ex- 
pelled by the dilatation due to the diminished pressure 
of the atmosphere ; but the aérostat soon plunges into 
regions where the temperature is much lower than that of 
the strata of terrestrial air which it has left. The cold 
contracts the gas, the balloon loses its ascending power 
and descends. To maintain it at the level it has reached, 
it is necessary to diminish the weight, and the aéronaut 
throws out ballast. If he passa first night at great alti- 
tude, it is certain that he will be thus obliged almost con- 
tinually to lighten his craft. Next morning, as the sun 
rises, the bright burning rays heat the gas contained in 
the aérostat. The balloon, which had partly collapsed 
during the night, begins to fill out, the loose material 
stretches like the head of a drum, and it mounts into the 
higher regions of the atmosphere. It is now that the 
aéronaut will feel the want of a portion of the ballast he 
was obliged to cast away during the night. If the sun is 
hot, the balloon will rise so high that it will be necessary 
to moderate its ascent by letting off some of the gas. 
During the second night the reverse process takes place. 
This time the aéronaut has no longer the same 
resources as before ; the ballast, which is his life, is being 
continually exhausted. I willingly admit he may have 
sufficient for the second and even for the third night; but 
will he have enough for the sixth and seventh night, if 
the differences of temperature of day and night are con- 
siderable, as is probable? The moment will soon come 
when the sacks of sand will be empty ; the balloon will 
descend without any means being able to hold it back, 
But instead of encountering a hospitable soil, it strikes 
against the crest of the waves. The anchor instead of 
biting, will plunge in vain in the waters ; if the wind is 
violent, in spite of their life-boat, the voyagers may be 
prepared for a most horrible fate. The aérostat will be 
piteously raised by the wind, and the terrified train will 
shoot from wave to wave over the surface of the ocean. 
Unusually clever will be the men carried along by such a 
force, if they could manage to find the means of detach- 
ing the life-boat.” 
It is certainly true that it would be very difficult to 
sustain a balloon at a considerable elevation for six days 
(if the height of the balloon is a matter of indifference, 
the guide rope as used by Green would be quite sufficient 
