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— charge the static accumulated on the ship. Laboratory tests wore made by the National Bureau of Standards of the electrical con- ductivity, at various humidities, of @ s¢ct- tion of the bow port trail rope, to determine whether the static discharge accumulated by the airship was or was not discharge when such rope made contact with the ground. Under the varying conditions em- ployed in the testa, it-was found that the alrzhin would he 00 percent discharged in a period of from 0.6 second to 170 scconds after such rope came in contact with the ground, With res to the potential gradjent ex- Jeting in the atmospbere in which the ship was standing, witnesa F. W. Reichelderfer, naval aerologist, indicated that conditions were favorable to a steep potential gradient due to the existence of a thunderstorm con- dition. Witness Eckener also believed thet a high potential adient existed at the time and place of the accidiyt, He ap- rently based his opinion oie the ,fol- lowing ; That a thunderstorm fivot had’ just passed over the station; that the heavy rain had become a light drizzle, thus re- ducing the potential gradient . materially and that from his information the appear- ance of the sky showed a light stratus ceil- ing. He proceeded to say that if one ciuse- ly examined the current registrations of winds, temperatures, and pressures, then one might recognize that the firat thunder front must bave had 4 smaller, lighter one following jt, that the wind turned back to the southeast. Winde of the higher alti- tude remained westerly. The rometer eurve showed a slight falling off of pres- gure and relatively the temperature started to Tise again, That ia, after the tempera- ture bad been brought down appreciably. by the breaking in of the cold alr, the temperature remuined constant for one-half hour before the landing maneuver to one one-half bour after the landing maneuver. Then the temperature again started to de- eline rapidly and the wind slowly turned back to the northwest. This, according to the witness, the esens!- tive instruments show, and that if this was not boticed at the fleld it was quite natural because attention wag focused on the Jand- ing Maneuver and on the bandling of the ship. (For registrations made by the sen- sitive inatruments, referred to by witness Eckener, see appendix 47 containing graphs Made at the naval air station, Lakeourst, XN, J., May 6, 1937, including anemograph, thermograph and micro-barograph traces— correct within 5 minutes.) He stated confidently that there waa a small tail-end to the first thunderstorm that passed by, which most likely created a steeper potential gradient than would oth- erwise be expected. Whether this stronger gradient could have generated suffictent po- tential between the airship and the air masses above the ship so that an equaliza- tion of the gradient tock place, either by St. Elmo’s fire, or by a spark, he was un- able to decide. ‘That the ignition was pot effected by such a static equalization spark immediately after the landing lines had been dropped was because they then were dry, hence poor con- ductors. They slowly became damp in the ght drizzle that was falling, and In such eondition their conductivity became greater. Therefore, he belleved that the potential between the ship and the ground was slowly equalized and afterward the potential gradient between the ship and the overly- ing air space was auiicient to generate these static sparke. Witness Whitehead, In commenting upon | ence. AIR COMMERC JDLLETIN J em, aid that if s secondary storm was present in sufficient intensity to cause & spark of lightning of any character that it would have been visible or audible. At any rale it would be reasonable to suppose that probably because of the pr ing thunderstorm ibe potential gradient at the time and place of the accident was some- whnt greater than norma). Witpesa F. A. L. Dartsch, aerologiet at the naval alr station, appeared to have a somewhat different opinion. He stated that previous to the landing there had been avy showers which could bave produced a strong potential dient but whether that stiH existed at time of the accident when only a light rain waa falling with just the clouda above, he could not definitely say. He did not believe that the potential radient then existing wae dangerous to the ship but be had no way of verifying his view. In answer to the question, “After the thunderstorm had disappeared, and the wind and rain had decreased, were there any signa or indication of a pew smal] deprea- sion or squall?” Witness Dartach sald that the only indication they bad had was the temporary shift from southeast to southwest with the elight—about one-hundredth inch— rise in pressure. However, no distinctive clouds of precipitation occurred with this change. Bruch discharge ordingrily im seen only after dark. It is manifested particularly from sharp pointa or projections of any material object that ia charged to a suffi- clently high electrostatic potential ao that the charge dissipates. The effect is pro- duced by particies of the material substance or by {onization of the gases of the atmos- Phere from impacts or stress. The ignition of a combustible mixture of gases In such a discharge is due to transformation of ki- netic energy {nto heat from impacts of jons or particles. The brush discharge appears either reddish or bluish depending upon the electrical sign of the charge. During the course of the public besrings, the question of whether a brush discharge would produce sufficient beat to ignite an inflammable hydrogen sir mixture, was dwelt upon to a considerable extent. Since that time, further experiments have been made in the high-voltage laboratory of the National Bureau of Standards and it bag been found possible to ignite hydrogen by a brush discharge by ysing somewhat more jutense discharges than those previously tried with a somewhat slower velocity of the gas passing the needle point. In thia consideration of the possibility of brush discharge it te to be noted tbat no witness testified that a visible indication of it was present. This, however, may be aecoubted for by the fact that darkness had not yet falien at ithe time of the accident. Witness Whitehead was of the opinion that the continuous presence of brush dis- charge, sufficient to cause the ignition, would require a greater current intensity than could have been possible through a dry rope. Another argument against_the brush dis- charge theory advanced by Witness White- head was that there wag much evidence that the first sign of fire was through the trans- Tyeent skin at the point well away from the tip of the fin. Witness Dieckmann in elaborating on this phenonemon stated that a one-hundredth or one-thoussndth part of a watt, perhaps legs, wae all that would be necessary to ignite a mnizture of air and hydrogep; that it was difficult for him to believe that brush dis- charge Was responsible for the ignition; that none of the witnesses testified to its pres- He remarked upon the testimony aa these views respecting the potential gradi- ‘to the presence of glowing reflections of