284 MEASUREMENT OF HIGH TEMPERATURES. [bull. 5 
the final experiment have been identical within 20° at 1,000°. Takin; 
the transpiration data alone they manifest a striking degree of accord 
auce even above 1,300°, as may be readily proved by the earlier tables 
81 to 85. Again the uniformity of variation of a given thermal datum 
whether measured thermo-electrically or by the transpiration pyrome 1 
ter, proves beyond a doubt that high thermal data are measurable a 
1,000° in terms of the viscosity in gases with an accuracy of a few tenths 
of a degree. 
TRANSPIRATION NOT SUBJECT TO THE POISEUILLE-METER LAW. 
Objects of tlie investigation. — The chief difficulty in operating with capil- 
lary tubes of a bore so fine that Meyer's formula is rigorously applicable 
at low temperatures as well as at high temperatures lies in the fact tha^l 
the flow in such tubes almost ceases when the degrees of white heatl 
are approached. There are a number of ways of obviating this annoys 
auce, in the first of which fascicles of tubes are used side by side; \ik 
the second of which the transpiring volumes are measured in gradecj] 
apparatus, so that at high temperatures small volumes may be measurecfil 
as accurately as large volumes at low temperatures. Again, tran spiral 
tion may be allowed to take place through graded capillary tubes ol 
platinum the length or bore of which increases by some given law ; oni 
with the slow current in continuous flow, rates of transpiration ( ~ ][ 
may be measured by some applicable method of repetition. 
It is nevertheless desirable, however well these means suffice forj 
the attainment of the end in question, to try to arrive at practical 
results relative to tubes of a bore so large that Meyer's formula is noj 
longer applicable. All these endeavors are decidedly in the interest of] 
expeditious work, for I find that compared with each other such meas-j 
urements are not lacking in accuracy, although the total time consumed 
for observation may not exceed a minute. 
To make these observations greater volumes of air are necessary.; 
Hence I have found it desirable to measure the volumes before they* 
enter the platinum capillary tube. I mention this here to point out an 
important peculiarity of the above apparatus. It is easily possible sol 
to adjust it that the gas may be measured both before entering and! 
after leaving the platinum capillary. The observer then has it in his 
power not only to detect the presence of gross leaks in the apparatus 
with certainty, but to follow the gas in its motions either (normally) 
through the capillary canal or (by diffusion) through the white-hot walls 
of platinum tube. 1 Moreover, it will be noted that the experiment in j 
gaseous flow through capillary tubes are accompanied by something re-] 
motely similar to self-induction on opening and on closing the circuit. For ; 
when the stop cock Jfin Fig. 45 is opened, the air rushes in the dead space. 
1 See remarks relativo to impure hydrogeD, p. 275. 
(938) 
