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back to earth. In two experiments the electroscope chmbed to 

 heights of 11.2 and 15.5 kilometres, heights to which it seemed (until 

 last year) that no man could possibly ascend and live. The apparatus 

 (there were four of them) had to make its own records and bring them 

 back; it was a masterpiece of ruggedness and compactness jointly, 

 as one sees in Fig. 7, on the left of which it appears assembled (with a 



Fig. 7 — Electroscope used in high-altitude measurements of cosmic rays by Millikan 

 and Bowen (photographs somewhat retouched). 



six-inch rule beside it to show its scale), on the right resolved into 

 disjecta membra. The symbol B marks a manometer in the form of a 

 U-tube with one arm closed, containing liquid; the symbol T, a 

 thermometer in the form of a coil of metal with a pointer at its end. 

 The light of the sky imprinted images of the meniscus of the barometer- 

 liquid and the pointer of the thermometer-coil upon a moving film, 

 kept in motion by the watch of which the mechanism is marked by W. 

 Inside the cylinder AT (so at least I read the text) were the two fibres 

 of the electroscope already shown as Fig. 1, and they also were con- 

 tinually photographed by the light of the sky upon another film which 

 the same watch kept in motion. 



When one of these devices had ascended to 15.5 kilometres (nearly 

 ten miles) and returned to earth eighty miles away from its starting- 

 point, and had been picked up (by some casual wanderer, one infers) 

 and returned to its authors, the films bearing the records of tem- 

 perature and fibre-divergence looked as they do in Fig. 8. To deter- 

 mine the extent of the ionization at great heights without being de- 



