349 
of Edinburgh, Session 1873-74. 
ing, rapid reabsorption takes place, and the tube is rendered again 
impervious to tbe discharge. This operation may apparently be 
repeated ad infinitum with the same results. 
Many important determinations may be effected through tbe em- 
ployment of carbon vacua, such as the temperature at which 
dissociation takes place between the carbon and the dissolved gas, 
tbe time required for reabsorption, and the effect of different gases 
in influencing tbe action of the carbon. We need hardly say that 
this easy means of obtaining vacua will be of importance in spec- 
troscopic observations, and we intend shortly to communicate 
observations in this direction. 
5. Laboratory Notes. By Professor Tait. 
1. On Atmospheric Electricity. 
For some days past I have been in tbe habit of observing atmo- 
spheric electricity about one o’clock, with the view of ascertaining 
whether the concussion produced by the time-gun has, as I 
suspected from an experiment of ten years ago, an effect on the 
amount collected by the water dropper. For several successive 
days the atmospheric charge was small and only slowly variable, 
and uniformly on these occasions I found a sudden slight increase 
of the deflection of tbe electrometer (whether it was originally 
positive or negative) to occur simultaneously with tbe sound, 
precisely the result obtained in the single experiment of date 21st 
May 1864. It appears to be most probably due to mere shaking 
of the instruments. 
On Thursday last, the 26th, during the great storm, the amount of 
electricity collected was so large, as in general to be beyond the range 
of my divided ring electrometer after a fraction of a second. I there- 
fore connected the water dropper with a gold leaf electroscope, whose 
leaves were thick, and about five inches long by one broad. These 
leaves are made to diverge so as to touch the tinfoil coating of 
the case in periods often less than a quarter of a minute, indicating 
a potential of, roughly speaking, many thousand G-rove’s cells. 
The most curious phenomenon, however, was this, that at intervals, 
often not exceeding a minute, and while rain and hail were 
alternating, the charge of tbe electroscope, even on this large 
