84 REPORTS ON THE STATE OF SCIENCE. 
thermometer pen lever is pivoted to the two free ends. The expansion 
or contraction of the German-silver strip causes the thermometer pen to 
move at right angles to the pressure traces. The traces are marked by 
two sharp steel styles on a roughly silvered metal plate. The scale of 
the instrument is :— 
1 mm. mercury = about 0°04 mm. deflection. 
11°C. = ,, 0:02 mm. deflection. 
The instrument with its case of polished aluminium, open at both ends, 
weighs only 55 gms. 
III. (6)—Testing of Instruments. 
Kite Instruments —The barometer of the Richard, Marvin, and 
Hergesell-Bosch kite instruments is tested under the receiver of an air- 
pump, by exhausting in steps. The pressure at each step is indicated 
by a mercury manometer. The barometer error due to temperature 
change is inappreciable at the heights reached by kites for the majority 
of the instruments. In those for which this is not the case, either a 
correction is applied as subsequently described for ballons-sondes instru- 
ments, or the aneroid or tube is replaced. In the case of the Dines instru- 
ment, however, the effect of temperature changes on the partially 
exhausted aneroids is considerable, owing to the contraction of the enclosed 
air and the comparatively thin German-silver walls of the box. The 
temperature correction is determined by placing the instrument in an 
alcohol bath, which may be cooled by carbonic-acid snow, and exhausting 
in steps at various temperatures. 
The method is rendered clear by the following table :— 
Temperature | Height Indicated Corrected Height Correction 
HOF Metres Metres Metres 
51 0 0 0 
610 610 0 
1220 1235 15 
1830 1845 15 
2440 2470 30 
3050 3080 30 
0 — 490 0 490 
0 490 490 
610 1110 500 
1220 1720 500 
1830 2350 520 
2440 2960 520 
3050 3580 530 
10 — 820 0 820 
i 0 820 820 
610 1450 840 
1220 2060 840 
1830 2680 850 | 
2440 3290 850 
3050 3900 850 
—20 —1170 0 1170 
0 1170 1170 
610 1780 1170 
1220 2410 1190 
1830 3020 1190 
2440 3640 1200 
3050 4250 ; 1200 | 
