242 MEASUREMENT OF HIGH TEMPERATURES. [bvvL 
cosity of a number of gases are studied between —21° and 280°. IV 
Holman's later researches go as far as 224° for 0O 2 and 124° for air. 
Wiedemann observed in thermal baths of steam (100°> and anili 
vapor (185°). Hence, if the transpiration data are eventually to su 
serve the purposes of temperature measurement, it is necessary in ti 
first place to investigate the law of variation of viscosity and tempei 
ture for a range of variation extending above 300° as far as possib 
into the region of white heat. 
Since this law is necessarily a fundamental consideration it will be i 
expedient to report my work in the chronological order of developmer 
It will be preferable, first, to give such results as have an immediat 
bearing on the law in question, and then to extend the work by i 
investigation of the flow of gases through tubes to which the ter 
"capillary," taken in the sense of the conditions under which Meyei 
formula holds, does not strictly apply. For very short tubes Navie 
investigated the theory of efflux ; for very long tubes these conditio] 
are equally well known from the stated investigations of Poiseuille at 
Meyer. For tubes of intermediate dimensions, however, the inform 
tion in hand is comparatively meager, although recent investigations 
a relevant character have been published by Osborne Reynolds, 2 I 
Guthrie, 3 and by Hoffmann. 4 
TRANSPIRATION SUBJECT TO THE POISE UILLE-ME FEB LAW. 
APPARATUS. 
General disposition of parts. — The great degree of perfection whic 
Professor Eichards 5 has attained in his jet aspirators suggests the m 
of this apparatus in the present experiments in a manner similar 1; 
that employed by Holman. Such adjustment was at first contemplate! 
lieasons, however, into which I need not enter here, together with tl 
fact that in some of the experiments larger pressures were demandc 
than those which the jet-pump could furnish in our laboratory, led 1 
the employment of absolute methods and of the special apparatus no 
to be described. It consists essentially of two large vessels, one place 
as far as may be necessary above the other and connected by wrappe 
rubber tubing. The upper of these vessels is filled with mercury an 
the lower contains the dry air to be forced through the train of capi 
lary tubes in connection with it. In this way a column of mercury < 
any desired height is brought to bear on the lower vessel, and the d< 
tails of adjustment are then to be such that this pressure may remai 
constant throughout the course of the experiment. 
! Navier : Me*ni. Acad. Roy. des Sc, vol. 9, 1830, p. 336. 
2 0. Reynolds: Roy. Inst. Gr. Brit., 1884, p. 1; Beiblatter, vol. 10, 1886, p. 217. 
3 Guthrie: Phil. Mag., 5th ser., vol. 5, 1878, p. 433. 
4 Hoffmann: Ann. der Physik, Wiedemann, new series, vol. 21, 1884, p. 470. 
5 Richards: Am. Jour. Sci., 3d series, vol. 8, p. 412; Trans. Am. Inst, Mining Eng 
neers, vol. 6, 1879, p. 492. 
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