VRUS.j 
PORCELAIN AIR THERMOMETRY. 
Table 77.— Permanent volwnie variations of bulb. 
233 
¥(t) 
|?xl0* 
vo 
Mean volumes 
vo 
Before Series I 
After Series I 
After Series II 
After Series III.... 
After Series IV 
After Series V 
72. G77 
73. 240 
73. 188 
73.210 
73. 180 
73. 188 
+ 6.98 
-0.71 
±0.00 
—0.30 
+C.11 
±0.00 
cc. 
281. 26 
279. 10 
279. 30 
279. 22 
279.33 
279. 30 
I 
cc. 
280. 18 
S 
I 
279. 20 
3 
I 
279.26 
S 
... 279.27 
....279.32 
5 
The values of v in the last column are therefore the closest approach 
o the respective zero volumes of the bulb during the successive series 
to V in question. It is this corrective which makes the results 1 of 
ig. 42 very much more uniform than those of Fig. 41. 
If Fig. 41 be compared with Fig. 42 it will be seen that the agree- 
lent of loci is very good. It is clear, beyond question, that the discrep- 
ncies involved are those incidental to the measurement; discrepancies, 
loreover, which are capable of considerable reduction by improving the 
xperimental appurtenances in the way suggested above. It therefore 
)Jlows that the degree of identity of the environment of the air thermom- 
ter and of the thermo couple is as nearly perfect as the calibration 
roblem demands. Again, from the difficulty I have found in obtaiu- 
ig accordance between different series of results in the earlier experi. 
lents, I believe that with the use of the present form of re-entrant bulb 
he calibration problem has for the first time been rigorously solved ; 
3r it is obvious that if the constants of either of the loci (Figs. 41 or 42) 
rere calculated by the method of least squares their probable error 
rould be decidedly within one promille. 
Boiling point of zinc. — This is the stage of progress at which my other 
uties will make it necessary to temporarily abandon the temperature 
►roblems and proceed toward a corresponding development of the press- 
ire work. I need merely notice therefore in what respects the ab- 
olute data of this chapter substantiate the earlier inferences. For 
Qstance, if the values of e 2() , which hold for the boiling point of zinc 
riven at the end of Chapter II, be interpreted by aid of the final dia- 
l A curious source of error may be noted here. When the centrifugal blower is in- 
ulated the friction of the belt electrifies it permanently. If, furthermore, the tubing 
ie insulated the furnace will be charged with a current of electrified air. Through 
he wires of the thermo-couple this charge is distributed over the measuring appara- 
us. If now, any metallic part of this (for instance, the metal of a rheostat key) be 
ouched with the finger there results a redistribution of the charge and invariably a 
arge deflection of the galvanometer needle. This is seriously misleading, and the error 
i not always at once detected. Care should therefore always be taken that the tube 
onveying air to the furnace from the blower is not insulated. # 
(887) 
