116 
In order to facilitate the application of the needful tem- 
perature corrections, it is desirable to secure the upper part 
of the barometer to the block of timber which supports the 
wheel, leaving the lower end free. There is also an advan- 
tage in introducing a small quantity of sulphuric acid into 
the small tube D, to promote the freedom of movement of 
the mercury in it. 
The average time occupied by an observation is found to 
be | of a minute, and the average error tsVo of an inch. 
In the morning of yesterday the wind was high and gusty, 
causing the mercury to oscillate at short intervals of time 
through a space of about 200 of an inch. 
Mr. C. H. Stearn exhibited and described a new form of 
portable Sprengel pump. In this arrangement all atmo- 
spheric pressure is removed from the mercury in the upper 
reservoir, and the lower receiver exhausted by a mechanical 
pump before the Sprengel is set in action. In consequence 
of the reduction of pressure on the reservoirs the length of 
fall tubes can be diminished to only a few inches ; the time 
occupied in exhaustion is also greatly shortened as the pre- 
liminary exhaustion of the receiver removes at the same 
time most of the air from the vessels attached to the upper 
part of the pump. In the earlier form of the instrument 
exhibited by the author at Plymouth the fall tube was 
single ; in the present modification this was divided into 
three branches, as in Mr. Giningham’s pump, and far greater 
rapidity was obtained in consequence. Exhaustions of 
O'OOOo mm. have been obtained with these pumps, and the 
spark from a 5 -inch induction coil has been completely 
arrested by a space of 8 mm. in the vacuum. A modifica- 
tion of M’Leod’s gauge was also described, adapted for use 
with the portable Sprengel. 
“ A Comparison of the Standard Barometer of the Owens 
College Physical Laboratory with the working Barometer/’ 
by Mr. Moris abro Hiraoka, Student of Owens College. 
Communicated by Professor B. Stewart, LL.D., F.B.S. 
