£70 Mr Harvey on the Methods employed for examining 
sidian stone *, as will appear from the oryctognostic description, 
made up from the specimens which I have in my possession. 
The colour of this stone was raven-black ; but on one sur- 
face of polished specimens there was an appearance of parallel 
streaks, of a somewhat paler colour. 
The form in which it occurs is subglobular, obtusely angu- 
lar, which is compared by Vincent to that of a potato. 
The size of the specimens is that of some inches in diameter. 
Lustre intermediate between pitchy and glassy. 
Fracture small conchoidal. 
Opaque, unless in very thin plates, which, in the light of a 
candle, are somewhat translucent, passing from grey to deep 
leek-green. 
Hardness very great, admitting a high polish. 
Specific gravity, £.410. 
All these circumstances, in short, demonstrate, that the genu- 
ine iEthiopic opsian stone, again discovered of late years, but 
hitherto seen by very few mineralogists, is identically the same 
with the common Obsidian , which used formerly to go by the 
improper name of Iceland Agate. 
Art. VII. — Account of the Methods employed for Examining 
the Population Returns of Plymouth for the year 18£1, and 
the consequent discovery of the Registered Seamen having been 
included in the Census of 1811, contrary to the terms of the Act 
of Parliament relating to the Population of the United King- 
dom. By George Harvey, Esq. M.A. S., M.G.S., &c. &c. 
In a note attached to the first part of my Essay on the Ame- 
rican Population, printed in the preceding Number of the 
Edinburgh Philosophical Journal, I briefly alluded to a plan 
which was successfully carried into execution at Plymouth, in 
the year 18£1, for ascertaining the population of that place, 
* c. f. Inprimis Andr. Libanii Singularium, p. iii. p. 796. — Salmasius in Soli- 
num, p. 91. 204.-^-C. de Caylus in Mem. de l’Acad. des Inscriptions, vol. xxx. 
p. 457. — Ad. Fabroni in Opuscoli scelti sulle scienze e sulle arte, t. xi. p. 369. — 
Andr. I. Retrii, Observ, de lapide obsidiano, Lund. 1799, 4. ; et Chr. Aug. Schwarze 
de Theophrasti Leparaco lapide, Gorlit. 1801, fol. 
