76 
Proceedings of the Royal Society 
remains of getting quit of the vitiated air produced in crowded 
assemblies. This also formed the subject of experiment in the hall 
by my having temporary wooden tubes, 12x6 inches wide, placed 
along the walls about 6 feet from the floor, and discharging outside 
the roof. These, in a crowded meeting, were found to he very effi- 
cient in carrying off the vitiated air, though occasionally a hack- 
draught came down ; hut were the discharge into a- cavity above the 
ceiling, or an archimedean can at the opening, the hack-draught 
would he avoided. 
I have perfect faith in the efficiency of these wall-tubes in carry- 
ing off the vitiated air, and may mention an attempt I made for a 
visible proof of this. I burnt brown paper to produce smoke. The 
smoke ascended only a few feet, and then spread out horizontally in 
a cloud, and when near any of the tubes it was drawn up. 
Remarks. 
In Table Ho. II. the course of the hot air on entering the hall is 
pretty well shown. The larger portion, of course, mounts towards 
the roof, along which it travels at somewhat different temperatures. 
Hot so, however, below where the audience sits, — there the gradu- 
ally-rising temperature is practically equal in all corners of the hall, 
and that without any appreciable difference in time between the 
effects on the several thermometers. 
2. Chapters on the Mineralogy of Scotland. By Professor 
Heddle. Chapter VI. “ Chloritic Minerals.” 
In this Chapter, Dr Heddle discussed the substances usually 
thrown together, under the term of Chloritic Minerals. He showed, 
by an extensive series of analyses, that they were to be divided into 
three groups — those which occurred in metamorphic rocks, in recent 
strata, and in volcanic rocks. 
He proposed to confine the term Chloritic to the minerals which 
are found in metamorphic rocks, and to apply the term, the Sapo- 
nites, to those which occur in volcanic rocks. 
In Scotland, metamorphic rocks afforded the species Pennina, 
Ripidolite, Chlorite, and Chloritoid. The Hew Red Sandstone of 
Elgin yielded Glauconite. Volcanic rocks contained, plugging up 
