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MICEOSCOPICAL AND NATUEAL HISTOEY SECTION. 
Ordinary Meeting, January 17th, 1887. 
Professor W. C. Williamson, LL.D., F.R.S., in the Chair. 
Mr. K T. Burnett, F.G.S., was elected an Associate of the 
Section. 
Mr. Henry Hyde exhibited a leaf of Bryojpliyllum 
calycinum, with young plants growing out of the margin. 
Dr. Alex. Hodgkinson read a paper On Cavities in 
Minerals containing fluid, with Yacuoles in motion, and 
other inclosures.” 
It is matter of common observation that salts in crystal- 
lising from their solutions frequently shut off spaces 
containing portions of the fluid. If at the time of 
crystallization the temperature of the liquid was higher 
than it subsequently comes to be, contraction of the fluid 
in the enclosed cavity takes place, and a bubble or vacuole 
is formed. The relative volume of the vacuole to the 
dimension of the cavity may be taken as a rough indica- 
tion of the temperature of the solution at the time of 
crystallization. 
The minerals most commonly containing fluid cavities 
