Five Weeks in a Balloon

CHAPTER SEVENTH.

Ge­omet­ri­cal De­tails.–Cal­cu­la­tion of the Ca­pac­ity of the Bal­loon.–The Dou­ble Re­cep­ta­cle.–The Cov­er­ing.–The Car.–The Mys­te­ri­ous Ap­pa­ra­tus. –The Pro­vi­sions and Stores.–The Fi­nal Sum­ming up.

Dr. Fer­gu­son had long been en­gaged up­on the de­tails of his ex­pe­di­tion. It is easy to com­pre­hend that the bal­loon –that mar­vel­lous ve­hi­cle which was to con­vey him through the air–was the con­stant ob­ject of his so­lic­itude.

At the out­set, in or­der not to give the bal­loon too pon­der­ous di­men­sions, he had de­cid­ed to fill it with hy­dro­gen gas, which is four­teen and a half times lighter than com­mon air. The pro­duc­tion of this gas is easy, and it has giv­en the great­est sat­is­fac­tion hith­er­to in aero­stat­ic ex­per­iments.

The doc­tor, ac­cord­ing to very ac­cu­rate cal­cu­la­tions, found that, in­clud­ing the ar­ti­cles in­dis­pens­able to his jour­ney and his ap­pa­ra­tus, he should have to car­ry a weight of 4,000 pounds; there­fore he had to find out what would be the as­cen­sion­al force of a bal­loon ca­pa­ble of rais­ing such a weight, and, con­se­quent­ly, what would be its ca­pac­ity.

A weight of four thou­sand pounds is rep­re­sent­ed by a dis­place­ment of the air amount­ing to forty-​four thou­sand eight hun­dred and forty-​sev­en cu­bic feet; or, in oth­er words, forty-​four thou­sand eight hun­dred and forty-​sev­en cu­bic feet of air weigh about four thou­sand pounds.

By giv­ing the bal­loon these cu­bic di­men­sions, and fill­ing it with hy­dro­gen gas, in­stead of com­mon air–the for­mer be­ing four­teen and a half times lighter and weigh­ing there­fore on­ly two hun­dred and sev­en­ty-​six pounds–a dif­fer­ence of three thou­sand sev­en hun­dred and twen­ty-​four pounds in equi­lib­ri­um is pro­duced; and it is this dif­fer­ence be­tween the weight of the gas con­tained in the bal­loon and the weight of the sur­round­ing at­mo­sphere that con­sti­tutes the as­cen­sion­al force of the for­mer.

How­ev­er, were the forty-​four thou­sand eight hun­dred and forty-​sev­en cu­bic feet of gas of which we speak, all in­tro­duced in­to the bal­loon, it would be en­tire­ly filled; but that would not do, be­cause, as the bal­loon con­tin­ued to mount in­to the more rar­efied lay­ers of the at­mo­sphere, the gas with­in would di­late, and soon burst the cov­er con­tain­ing it. Bal­loons, then, are usu­al­ly on­ly two-​thirds filled.

But the doc­tor, in car­ry­ing out a project known on­ly to him­self, re­solved to fill his bal­loon on­ly one-​half; and, since he had to car­ry forty-​four thou­sand eight hun­dred and forty-​sev­en cu­bic feet of gas, to give his bal­loon near­ly dou­ble ca­pac­ity he ar­ranged it in that elon­gat­ed, oval shape which has come to be pre­ferred. The hor­izon­tal di­am­eter was fifty feet, and the ver­ti­cal di­am­eter sev­en­ty-​five feet. He thus ob­tained a spheroid, the ca­pac­ity of which amount­ed, in round num­bers, to nine­ty thou­sand cu­bic feet.

Could Dr. Fer­gu­son have used two bal­loons, his chances of suc­cess would have been in­creased; for, should one burst in the air, he could, by throw­ing out bal­last, keep him­self up with the oth­er. But the man­age­ment of two bal­loons would, nec­es­sar­ily, be very dif­fi­cult, in view of the prob­lem how to keep them both at an equal as­cen­sion­al force.

Af­ter hav­ing pon­dered the mat­ter care­ful­ly, Dr. Fer­gu­son, by an in­ge­nious ar­range­ment, com­bined the ad­van­tages of two bal­loons, with­out in­cur­ring their in­con­ve­niences. He con­struct­ed two of dif­fer­ent sizes, and in­closed the small­er in the larg­er one. His ex­ter­nal bal­loon, which had the di­men­sions giv­en above, con­tained a less one of the same shape, which was on­ly forty-​five feet in hor­izon­tal, and six­ty-​eight feet in ver­ti­cal di­am­eter. The ca­pac­ity of this in­te­ri­or bal­loon was on­ly six­ty-​sev­en thou­sand cu­bic feet: it was to float in the flu­id sur­round­ing it. A valve opened from one bal­loon in­to the oth­er, and thus en­abled the aero­naut to com­mu­ni­cate with both.

This ar­range­ment of­fered the ad­van­tage, that if gas had to be let off, so as to de­scend, that which was in the out­er bal­loon would go first; and, were it com­plete­ly emp­tied, the small­er one would still re­main in­tact. The out­er en­ve­lope might then be cast off as a use­less en­cum­brance; and the sec­ond bal­loon, left free to it­self, would not of­fer the same hold to the cur­rents of air as a half-​in­flat­ed one must needs present.

More­over, in case of an ac­ci­dent hap­pen­ing to the out­side bal­loon, such as get­ting torn, for in­stance, the oth­er would re­main in­tact.

The bal­loons were made of a strong but light Lyons silk, coat­ed with gut­ta per­cha. This gum­my, resinous sub­stance is ab­so­lute­ly wa­ter-​proof, and al­so re­sists acids and gas per­fect­ly. The silk was dou­bled, at the up­per ex­trem­ity of the oval, where most of the strain would come.

Such an en­ve­lope as this could re­tain the in­flat­ing flu­id for any length of time. It weighed half a pound per nine square feet. Hence the sur­face of the out­side bal­loon be­ing about eleven thou­sand six hun­dred square feet, its en­ve­lope weighed six hun­dred and fifty pounds. The en­ve­lope of the sec­ond or in­ner bal­loon, hav­ing nine thou­sand two hun­dred square feet of sur­face, weighed on­ly about five hun­dred and ten pounds, or say eleven hun­dred and six­ty pounds for both.

The net­work that sup­port­ed the car was made of very strong hempen cord, and the two valves were the ob­ject of the most minute and care­ful at­ten­tion, as the rud­der of a ship would be.

The car, which was of a cir­cu­lar form and fif­teen feet in di­am­eter, was made of wick­er-​work, strength­ened with a slight cov­er­ing of iron, and pro­tect­ed be­low by a sys­tem of elas­tic springs, to dead­en the shock of col­li­sion. Its weight, along with that of the net­work, did not ex­ceed two hun­dred and fifty pounds.

In ad­di­tion to the above, the doc­tor caused to be con­struct­ed two sheet-​iron chests two lines in thick­ness. These were con­nect­ed by means of pipes fur­nished with stop­cocks. He joined to these a spi­ral, two inch­es in di­am­eter, which ter­mi­nat­ed in two branch pieces of un­equal length, the longer of which, how­ev­er, was twen­ty-​five feet in height and the short­er on­ly fif­teen feet.

These sheet-​iron chests were em­bed­ded in the car in such a way as to take up the least pos­si­ble amount of space. The spi­ral, which was not to be ad­just­ed un­til some fu­ture mo­ment, was packed up, sep­arate­ly, along with a very strong Buntzen elec­tric bat­tery. This ap­pa­ra­tus had been so in­ge­nious­ly com­bined that it did not weigh more than sev­en hun­dred pounds, even in­clud­ing twen­ty-​five gal­lons of wa­ter in an­oth­er re­cep­ta­cle.

The in­stru­ments pro­vid­ed for the jour­ney con­sist­ed of two barom­eters, two ther­mome­ters, two com­pass­es, a sex­tant, two chronome­ters, an ar­ti­fi­cial hori­zon, and an al­taz­imuth, to throw out the height of dis­tant and in­ac­ces­si­ble ob­jects.

The Green­wich Ob­ser­va­to­ry had placed it­self at the doc­tor’s dis­pos­al. The lat­ter, how­ev­er, did not in­tend to make ex­per­iments in physics; he mere­ly want­ed to be able to know in what di­rec­tion he was pass­ing, and to de­ter­mine the po­si­tion of the prin­ci­pal rivers, moun­tains, and towns.

He al­so pro­vid­ed him­self with three thor­ough­ly test­ed iron an­chors, and a light but strong silk lad­der fifty feet in length.

He at the same time care­ful­ly weighed his stores of pro­vi­sion, which con­sist­ed of tea, cof­fee, bis­cuit, salt­ed meat, and pem­mi­can, a prepa­ra­tion which com­pris­es many nu­tri­tive el­ements in a small space. Be­sides a suf­fi­cient stock of pure brandy, he ar­ranged two wa­ter-​tanks, each of which con­tained twen­ty-​two gal­lons.

The con­sump­tion of these ar­ti­cles would nec­es­sar­ily, lit­tle by lit­tle, di­min­ish the weight to be sus­tained, for it must be re­mem­bered that the equi­lib­ri­um of a bal­loon float­ing in the at­mo­sphere is ex­treme­ly sen­si­tive. The loss of an al­most in­signif­icant weight suf­fices to pro­duce a very no­tice­able dis­place­ment.

Nor did the doc­tor for­get an awning to shel­ter the car, nor the cov­er­ings and blan­kets that were to be the bed­ding of the jour­ney, nor some fowl­ing pieces and ri­fles, with their req­ui­site sup­ply of pow­der and ball.

Here is the sum­ming up of his var­ious items, and their weight, as he com­put­ed it:

Fer­gu­son……………………… 135 pounds. Kennedy………………………. 153 ” Joe………………………….. 120 ” Weight of the out­side bal­loon…… 650 ” Weight of the sec­ond bal­loon……. 510 ” Car and net­work……………….. 280 ” An­chors, in­stru­ments, awnings, and sundry uten­sils, guns, cov­er­ings, etc………………. 190 ” Meat, pem­mi­can, bis­cuits, tea, cof­fee, brandy………………. 386 ” Wa­ter………………………… 400 ” Ap­pa­ra­tus…………………….. 700 ” Weight of the hy­dro­gen…………. 276 ” Bal­last………………………. 200 ” —– 4,000 pounds.

Such were the items of the four thou­sand pounds that Dr. Fer­gu­son pro­posed to car­ry up with him. He took on­ly two hun­dred pounds of bal­last for “un­fore­seen emer­gen­cies,” as he re­marked, since oth­er­wise he did not ex­pect to use any, thanks to the pe­cu­liar­ity of his ap­pa­ra­tus.