108 



A. Z. Day and R. B. Sosman- 



Tlie length of the mercury column was reduced to 0° by the 

 expansion coefficient given in the Landolt-Bornstein-Meyer- 

 hoffer Tabellen. This correction varied from to about 3*00 mm . 

 As the mercury thermometers were calibrated and read to 0*1°, 

 the uncertainty in this correction due to uncertainty in the 

 room temperature may amount to 0'05 min . For the calibration 

 the mercury thermometers were compared with a Bichter 

 standard thermometer calibrated at the Reichsanstalt. 



The barometer reading was corrected to 0° by the Landolt- 

 Bornstein-Meyerh offer table for barometer with brass scale. 

 Two Fuess barometers were used. Both had been tested by 

 the Bureau of Standards ; one had an absolute correction of 

 0'06 mm , the other was exact. This was checked by direct com- 

 parison of the two. The variable error in the barometer is 

 probably about the same as in the manometer reading (0*05 mm ). 

 On a very windy day or during the approach of a storm, the 

 barometer was too unsteady to permit satisfactory measure- 

 ments to be made. 



A further small correction to the barometer was necessary to 

 allow for the weight of the air column between the cup of the 

 barometer and the top of the mercury in the open manometer 

 column. This correction was appreciable, amounting to 0*16 mm 

 in the extreme case. 



To give some idea of the effect of these small corrections 

 upon the h'nal temperature measurement, it may be added that 

 l # 00 mm corresponds approximately to 1°. 



To determine the corrected pressure, p, from the measured 

 pressure, %>' (seepage 101), the volume of the unheated space, v^ 

 connecting the bulb with the manometer, must be known. * 



Table I. — Unheated Space. 











Max. effect 



Space 



Volume, c.c. 



Uncertainty 



at Cu. pt. 











of errors 





Before 



After 



of vol. 



of temp. 







Apr. '00 



Apr. '09 









Pt-Rh capillary, bulb to top 













furnace (vi') 



0-055 



0-055 



0-002 



100° 



0-04° 



Pt-Rh capillary, top to out- 













side furnace (V) 



0-086 



0-086 



0-003 



50° 



0-20° 



Pt-Rh capillary to gold ~] 













capillary 



0-102 



0-0541 









Gold capillary ! ,,, 

 Pt capillary and Ni f 1 



0-094 



0-066 | 











y 



0-015 



0-5° 



0-20° 



valve 



0-025 



0-025 | 









Space above meniscus J 



0-023 



0-023 J 









Total 



0-385 



0-309 



0-45° 



*See discussion of this correction, Day and Clement, loc. cit., p. 410. 



