a 2) 
34 H. C. RUSSELL. 
sition is still doubtful, but he finds that a minute trace of some 
impurity, besides the nitrogen and mercury is probably necessary 
for its formation. At present the nature of the impurity has not 
been determined. The Professor finds “strie” in the purest 
tubes he has been able to make, but toa much smaller extent 
than in well purified gas, and he is now observing the gas in 
“endless tubes,” 2.e., tubes which form themselves the secondary 
of an induction coil. 
Some months were spent in trying to make the static gravity 
meter sensitive enough to show Lunar disturbances of gravity, 
but so far without success, even when using Michelson’s interfer- 
ence method on the scale which quartz threads permitted them to 
give to the size of the mirrors. A fixed instrument has been 
made which will show a change of antes ‘‘o” and efforts are 
being made to construct a portable gravity meter sensitive’ to 
sotoo “g,” with every prospect of success. Mr. Pollock is carry- 
ing on this work as he finds time. Important experiments on the 
electric properties of sulphur were begun in 1887 and are still in 
progress, and have led to curious results depending on the state 
of the sulphur. These demand a special galvanometer, which 
has taken a long time to make. It is required to investigate 
phenomena beyond the reach of ordinary instruments. Meanwhile, 
there is no doubt that pure sulphur is one of the best non-con- 
ductors known, and it is so far as Prof. Threfall knows at present, 
almost free from the phenomena of electric absorption, a property 
which may be of value. Mr. Brearley is assisting the Professor in 
this work. Experiments have been carried out on the change of 
temperature observed during the diffusion of gases, with results 
at present inexplicable. Mr. Farr is working at the magnetic 
elements. He observed the changes day and night for a week, 
and Mr. Knibbs has carefully laid down bearings with an eight- 
inch theodolite. The results are almost ready for publication. 
A marked change has taken place during the past four years. 
The Professor has devoted much of his time recently to the 
theory and practice of electro-magnetic reciprocating mechanisms 
