barus.] VISCOSITY OF GASES. 293 
Among these tables the first is unique, and I shall therefore specially 
refer to it. The capillary tube used is the same with which the data 
iii Tables 81 to 90 w r ere investigated; but for the large volume V G the 
time of efflux at red heat (977°) is five hours. During the whole of this 
time 6" and P were measured so as to obtain a fair mean result and 
eliminate unavoidable fluctuations of temperature. It is exceedingly 
gratifying to observe that the value of F (6") computed from these 
observations conforms very well with the data of Tables 81 to 89, and 
with the law ?/ / =fj (l-\-a(/"Y^ despite the great difference of method of 
measurement employed. Differences of t? q in different parts of the table 
are due to imperfections in the earlier adjustment; but the values of 
7/0 measured before and after the high temperature measurement agree 
satisfactorily. Yariations of ?j with P will be discussed below. The 
negative error of F{6") may also be anticipated, since in so long a 
period of efflux (five hours) even minute leaks in the compressing appa. 
ratus would produce appreciable results. 
Transpirations compared differentially. — Before proceeding with the 
discussion of these results it is expedient to communicate the data 
obtained with a differential apparatus. The formula for this method 
of experimentation has already been given. Hence the results of the 
following Tables 101 to 103 need but little further elucidation. The ad- 
justments here are identical in plan with those of the differential gal- 
vanometer. In Fig. 55, p. 305, air is supposed to enter at a and to pass 
through the stop-cock K, where the bifurcation of current is brought 
about. Supposing K open, a part of the air passes through the hot 
spiral R and thence to the measuring-tube V g ; the remainder through 
the cold helix (7, and thence to the measuring-tube V h . V h and V g cor- 
responding respectively to the temperature 6 and 6" are given in the 
Tables. If 6=6", then the results contain data for the computation of 
the ratio of the radii of the two helices.- If 6">6, the results lead to 
the beauty of the method being this, that time and pressure measure- 
ments (in the case of capillary tubes of very small bore) are superfluous. 
I have purposely used tubes of large bore however. From Fi(6"), 
'/(»£) 
may be calculated by inserting the corresponding values of ;/ from 
Tables 9G to 100. 
(947) 
