172 
DR. E. P. PERMAR, DR. W. RAMSAY, AND MR. J. ROSE-INNES 
time. During the breaking of the capillary point, the whole apparatus was tilted, so 
as to incline the experimental tube. The pressure was then raised so as to cause 
some mercury to enter the tube, which was then placed in a nearly horizontal 
position. By tapping, the silica was made to flow down, so as to form an evenly 
distributed layer in the experimental tube; the temperature was then finally 
adjusted, and after placing the mercury at a given mark on the tube, experiments 
were begun. At the temperature chosen the ether was wholly gaseous. On rubbing 
the projecting rod, the ether gas vibrated, and the silica arranged itself in heaps, 
which, wdien the ether gas wars at its greatest volume, amounted to over thirty in 
number. They w'ere, for the most part, regularly distributed. A millimetre scale 
etched on a slip of mirror, JK (fig. 1), wus laid below^ the experimental tube, and 
the distance between the heaps was read. But instead of reading the actual position 
of all the heaps an average was taken in the followdng manner:—Suppose the total 
number of heaps to be 30 ; the 1st and 27th were read ; the 2nd and 28th ; the 3rd 
and 29th ; and the 4th and 30th ; and, dividing by the total number read, four 
averages w^ere obtained. These usually agreed with each other to within 0'5 per cent. ; 
the mean of all four was taken as the true wave-length. 
The middle of each heap of silica wus taken as most easily read. The silica could 
hardly be said to form “heaps”; it distributed itself in streaks of varying length 
across the tube, each set of streaks forming an oval-shaped patch, of which the 
middle point could be estimated with fair accuracy. 
The volume of the gas w^as then diminished, and another set of readings taken in 
a similar manner. The mercury entering the tube covered up a portion of the silica ; 
but on again increasing volume it flowed away, leaving the silica as before. This, of 
course, made it difficult, if not impossible, to determine accurately the volume 
occupied by the ether gas ; for the volume of the silica wms an uncertain quantity. 
But the whole amount of silica wms very small, certainly not amounting in volume to 
0*5 per cent, of that of the ether. To compensate for this error, by one in the 
opposite direction, no correction was made for the increase in volume of the tube on 
rise of temperature. The error thus introduced is about the same order of magnitude 
and opposite in sign to that involved by neglecting the volume of the silica, and 
hence the two errors may be taken as compensating each other to some extent. 
iMoreover, the volume of one gram of ether at definite temperatures and pressures 
had been determined by Dr, S. Young and one of the authors ; and it wms necessary 
to know the actual volume merely for the purpose of deducing the weight. 
The volume of the gas was successively decreased, and observations made similar 
to those described. The temperature having been raised by increasing the pressure 
on the boiling liquid, a fresh set of observations w'ere made. It wars necessary, 
hov/ever, wdrenever the jacketing vapour w'as changed, to refill the tube, because the 
contraction of the ether, owdng to its condensation, brought the mercury into contact 
with, the rod, and filled the space between it and the inner wnll of the experimental 
