of Edinburgh, Session 1872-73. 
87 
Monday, 1th Ajoril 1873. 
Professor Sir WILLIAM THOMSON, Vice-President, in 
the Chair. 
The following Communications were read : — 
1. Notice of a Singular Property exhibited by the Fluid 
enclosed in Crystal Cavities. By Edward Sang, Esq. 
The subject of the following communication is a phenomenon 
unexpected and peculiar ; it presents analogies to the phenomena 
of magnetism and electricity, in so much as it is an exhibition of 
repulsion ; but it is distinguished from these by the absence of at- 
traction, or what is called polarity. So far as I am aware, it is the 
only known example of repulsion exhibited independently of mag- 
netic or electric excitement, and seems to open up an entirely new 
field for physical research. On these accounts I was exceedingly 
desirous to have it brought without delay to the notice of scientific 
men, and I have to thank our Secretary for giving me the present 
opportunity, although at the inconvenience to him of it having to 
accompany a long and interesting paper on another subject. 
I shall confine myself this evening to a simple statement of the 
nature of the phenomenon, to its exhibition, and to an account of 
the circumstances that led to its discovery, reserving for anothei 
opportunity a more detailed notice of those observations and ex- 
periments that have already been made in regard to it. 
While discussing, along with Dr James Hunter, the occurrence 
of polished cylindric strise in calcareous spar, and while examining 
those striae under the microscope, I happened to notice an air- 
bubble in a minute cavity, having a regularly crystallised form, 
which air-bubble was found to move when the position of the spar 
was changed. 
Next forenoon, while showing this, in itself very interesting, 
matter to my pupil, Mr David A. Davidson, I desired to mark 
the position of the speck, and applied the point of my penknife to 
scratch the spar. Immediately the air-bubble was seen to move 
rapidly. My first thought was to attribute this motion to the pres- 
sure on the thin lamina of spar immediately above the cavity, but 
VOL. VIII. 
M 
