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PRESENT STATE OF OUR KNOWLEDGE OF THE UPPER ATMOSPHERE. 89 
accepted by observers as sufiicient. Experiments have been made in 
which the barometer, by completing an electric circuit at a given low 
pressure, set into motion a ventilating fan, producing a current of 
3-4 m.p.s. No discontinuity in the temperature trace was produced, 
showing that the effect of radiation in the isothermal zone was negligible 
under the conditions of the ascent.' It is also found that instruments 
of different types sent up together give results which are in good agree- 
ment. Thus in comparisons of the bimetallic thermometer of Teisserenc 
de Bort with the tube thermometer of Hergesell, the maximum difference 
between the temperatures indicated was 7°°3C., and the average difference 
was about 2° C. 
Comparisons of the Hergesell-Bosch with the Assmann instrument 
gave a maximum difference of temperature of 4°71 C. and a mean 
difference of 1°°7 C. 
The maximum difference between the temperatures indicated by two 
sa instruments sent up from Manchester was only 4° C. and the average 
only 1°C. 
Tables typical of the comparisons of various instruments are given. 
Comparison of Hergesell and Teisserenc de Bort Thermographs.* 
Temperature Temperature 
Height , _|| Height 
Hergesell L. T. de Bort Hergesell L, T. de Bort 
Km. Km. 
1 + 1:2 + 1:2 C — 33:0 — 33-4 
2 — 25 — 27 8 —39°8 —40°2 
3 — 49 — 49 9 —47°5 — 48-0 
4 —115 —11'8 10 —54:5 —55°5 
5 —18°5 —19:0 11 » = 59-4 —612 
6 —26°3 -—27-1 12 — 60-9 — 62:9 
Comparison of Hergesell and Assmann Thermographs. 
Temperature Temperature 
ee ee erony 
- Hergesell Assmann Hergesell § Assmann 
Km. Km. 
1 99 7-0 10 — 53:3 —52°8 
2 38 - 0:0 11 —51:3 — 52:1 
3 — 2-4 — 66 12 —50°8 —52°0 
4 — 9:2 —12°8 136" | —50°6 | —52°5 
5 —16°8 —19°9 14 —514 | —51°9 
6 —25°7 —29°8 15 —54:7 | —517 
ul —35:0 —38°6 16 —53°3 —517 
8 —44:5 — 48:2 17 —52°4 —518 
9 —54:5 —53°9 
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1 Ergeb. der Arbeit. am Aér. Obs. Lindenberg, 1907, p. xiii. 
2 Tbid., 1906, p. 103. 3 Lbid., 1905, p. 99. 
