IMPERIAL STANDARD TROY POUND WEIGHT. 
467 
because in tubes of so large a diameter there can be no uncertainty in the value of the 
small correction for capillarity. For the comparison of the two pounds, it is of little 
consequence what correction is employed, + 0066 inch or + 0 - 057 inch. It is un- 
necessary to add, that -j-0'057 inch involves the correction for capillarity and for the 
zero point of the scale ; so that after having applied it, the heights given by the baro- 
meter may be considered as absolute heights. 
11. The thermometers employed were small thermometers with ivory scales made 
by Messrs. Troughton and Simms, both suspended in the case of the balance near to 
the two ends of the beam. The thermometer marked L was at the left hand of the 
observer, the thermometer marked R at the right hand. I could determine only the 
corrections of the thermometer R, because the thermometer L was found to be broken 
when it arrived in Altona. Of course all its indications ought to be left out ; and 
the temperature, during the observations, is only to be taken from the readings of 
the thermometer R. 
For ascertaining its corrections, I employed two excellent standard thermometers ; 
one the present of the late Mr. Troughton, which he had constructed expressly for 
me, the other the present of Professor Bessel, the corrections of which he had with 
great care determined, according to his method. Both standards have the Fahren- 
heit scale. The scale of the thermometer R being of ivory, I could not compare it 
with the standards in water, but I brought its bulb in contact with the bulb of the 
standards, and enveloped both bulbs in a thick cover of down. I found by 
o o 
Troughton’s standard at 69 - 8 the corr. of R = — 0‘70, by 16 comp, made on 4 days. 
at 63 - 3 = — 0 6 1, by 16 comp, made on 7 days. 
Bessel’s standard at 64‘2 = — 0‘64, by 10 comp, made on 5 days. 
The correction given by Bessel’s standard agrees within 0 o- 02 with that given by 
Troughton’s standard. Upon these data I have constructed the following small 
Table of corrections to be applied to the thermometer R. 
Correction, 
o o 
63 = - 0-61 
64 = - 0-62 
65 = - 0 63 
66 = - 0-65 
Correction. 
o o 
67 = — 0-66 
68 = - 0-68 
69 = - 0-69 
70 = - 0 70 
12. It remains only to state how the observed heights of the barometer have been 
reduced to absolute heights at the temperature of 32°. I have for this purpose em- 
ployed a table, which will be given in my “ Jahrbuch fur 1837,” constructed upon 
the formula, 
Barometer reduction to 32° = h 
m ( t — 32 °) — s (t — 62 °) 
] + m [t — 32 °) 
where h denotes the height read off in English inches from the brass scale, which 
represents English inches at the temperature of 62°, m the expansion of the mercury 
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