1 0 0 D O C U M E N T 8 7 O C T O B E R 1 9 2 5 I plan to ascend to 3,000 m a[bove] s[ealevel]. 2/3 atmospheres prevail there. I can procure a balloon of 2,200 m3. If I can fill it with technical hydrogen, I arrive at the foll[owing] weights: carrying power to 3,000 m 1,550 kg balloon weight + equipment 550 kg " " of pilot + pers. equip. 100 " " " of 2nd ring & small basket 50 " " " maneuvering ballast 50 " Instrument 750 " 1,500 kg If only coal gas were taken, the available load would be 400 kg less. Then only 350 kg would remain for the instrument. One could settle for 2,000 m (however this would have the disadvantage that any mountain would compel a landing), which would still be 250 m higher than Mount Wilson. The pressure is 590 mm Hg there. Coal gas would then carry 1,300 kg we have 550 kg available for our instruments. Coal gas would have the advantage that it is available any time in Zurich. In Swit- zerland it is only possible to ascend with hydrogen from Thun but one must order it 24 hours in advance, which is tricky because of the weather. I am holding out for completely calm, anticyclonic weather conditions for the trip & the landing with the apparatus. Perhaps the Confed[erate] Military will place a tether balloon at my disposal [4] then one could fill up anytime from Bern. I could possibly depart from Bitterfeld, Brussels, or Friedrichshafen, if I get enough recommendations. This should be discussed precisely once I know the weights of the accumulator batteries & the thermostat better. I am [now] first going to concentrate entirely on the instrumental part. As soon as I am persuaded that I am equal to the task, I shall try to find funding for the trip. For this latter business, your moral support will be necessary to me. Please pardon me for having written you such a long letter but all the details would not easily be treated more briefly. With my best regards, respectfully yours,