terms, although they are not only totally useless, but even incorsistent with the leading principles upon which he arranges his families and species. Thus, we find in the class of earths, substances which contain no earth; in the class of metals some which would be more properly ranked among inflammables; and in the saline class, bodies which are not salts. The aid of chemistry being rejected in all the subordinate classification, we would also reject it in the highest; and by this means clear away, from the foundation of the mineralogical system, every thing but that whereon it seems to be the most securely established the external characters of mineral bodies.

The plan of the work now under consideration is, first, to give the synonyms, or various appellations which different writers have applied to the same substance: then to give its external characters; its chemical characters; constituent parts; its physical characters; its geognostic situation, or the formation, strata, and rocks, in which it is usually found; its geographic situation, or the country in which it occurs; its use; and lastly observations not coming under any of the foregoing heads. An example, however, will make all this better understood, which we shall give in the case of precious opal, the tenth species of the quartz family. After giving the synonyms of Pliny, Werner, Hauy, Kirwan, and others, he proceeds to

66 EXTERNAL CHARACTERS.

"The most common colour of precious opal is milk-white, inclining to blue, which, when held between the eye and the light, appears a pale wine-yellow. It seldom occurs yellowish-white. Sometimes it is accidentally coloured brown. It almost always displays a beautiful play of colour. The colours it throws out are blue, green, yellow, and red. Generally several of these colours appear in one piece; those specimens are rarer that exhibit but one colour, or where one colour preponderates over the others. The rarest and most beautiful of these colours is the red *. It occurs massive, disseminated, in plates, in strings, or in small veins. Internally its lustre is generally splendent, seldom passing into shining, and is vitreous. The fracture is perfect_conchoidal. The fragments are angular, and very sharp edged. It is translu cent, and then exhibits a red and green play of colours; or it passes from translucent into semitransparent, when it exhibits a most beautiful yellow colour; or it is semitransparent approaching

*The play of colours is caused by numerous minute rents that traverse this mineral; thin layers of air are contained in them, and these have the property of reflecting the prismatic colours. It is a phenomenon analogous to the coloured rings observed by Newton."

to

to transparent, when the principal colour is azure blue. It is semihard in a high degree. It is brittle. It is uncommonly easily frangible. Some varieties adhere more or less to the tongue.— Specific gravity 2.114, Blumenbach; 2.073, Karsten; 2.110, Brisson.

CHEMICAL CHARACTERS.

"Before the blow-pipe it becomes opaque and milk white, but it is infusible.

Opal of Czscherwinetza, according to Klaproth.

GEOGNOSTIC SITUATION.

"It occurs in small cotemporaneous veins in clay-porphyry, and is generally accompanied with semi-opal. It would appear also to occur in flætz amygdaloid, and in minute portions in veins in gneiss.

"GEOGRAPHIC SITUATION.

"It is found in great abundance in clay-porphyry at Czscherwenitza, near Kaschaw, in Upper Hungary; sparingly in floetz amygdaloid in the Feroe islands; and in Flatztrap rocks, in the north of Ireland, at Sandy Brae. Formerly small portions of it were found in the mines near Freyberg, in Saxony. Dr. Dree mentions that it occurs also in South America.

26 USES.

"The only opal mines in the world are those of Czscherwenitza, in Hungary, which have been worked for a long time: even so early as towards the end of the fourteenth century, about three hundred men were employed. This mineral, on account of its beauty and rarity, is considered by jewellers as a gem, and is worked into ring-stones, necklaces, ear pendants, and other ornaments. It is cut into a convex form, or en cabochon, as this form shews its colours to the greatest advantage: as it is soft, it should not be facetted; but if facets are cut on it, these ought to be very flat. The cutting is done on a leaden wheel, with tripoli and water; and then the opal is rubbed with tin ashes on a piece of chamois leather, by which operation it receives its perfect lustre. When it is deficient in colour, jewellers are in the practice of setting it in a foil of the desired colour; but if it exhibits a beautiful play of colour, it appears to the greatest advantage when set in a black case. At present the opal is held in high estimation in all countries, but particularly in Hungary, Moldavia, and Wallachia, where it forms the chief ornaments in the dress of the oldest and most wealthy families. It was much prized by the ancients. Pliny (the only one of the ancient writers who mentions the opal) describes it as

uniting

uniting the beauties of the carbuncle, amethyst, and emerald; and the Greeks expressed their admiration of this lovely gem by calling it paederos. Nonius, a Roman senator, possessed an opal of extraordinary beauty, valued at 160,0001. rather than part with which to Mark Antony, he chose to suffer exile.

"OBSERVATIONS.

"1. The peculiar play of colour distinguishes this mineral from all others. In all other characters it nearly agrees with common opal, differing principally in its higher degree of lustre and transparency.

"2. This is one of the few minerals whose name has remained unaltered from the earliest times; but its origin or derivation is imperfectly known. Some derive it from the Greek words of os, which signifies the eye or vision, because it was supposed to have the property of strengthening the eyes.

"3. The finer varieties are named Oriental opal. Tavernier, however, informs us, that no precious opal is found in the east, and that those which are sold as oriental are brought from Hungary.

"4. Those varieties of precious opal that adhere to the tongue are only translucent, and scarcely exhibit any of the play of colour which so remarkably distinguishes the common varieties; but when immersed in water, they become more transparent, and acquire a very beautiful play of colour. This property occurs also in some varieties of common and semi opal; and the older and some modern mineralogists considered these varieties as constituting a particular species, to which were given various names, as oculus mundi, hydrophena, or changeable opal. In order to preserve their beauty, we must be careful never to immerse them but in pure water, and to take them out again as soon as they have acquired their full transparency. When these changeable opals are weil dried, and immersed in melted wax or spermaceti, they absorb a portion of it, and become transparent, but on cooling become opaque again. For some time these prepared opals were imposed on the public as rare and singular minerals, and sold at a very high price, under the name of pyrophane.

"5. in the Imperial cabinet at Vienna, there are two pieces of opal from the mines in Hungary, which deserve to be mentioned here. The one is about five inches long, and two and a half in diameter, and exhibits a very rich and splendent play of colours; the other, which is of the shape and size of a hen's egg, is also extremely beautiful."

This extract gives a fair specimen of the style and plan of the work. It is full of information valuable to the mineralogist, whether practical or scientific, and it is expressed in language singularly perspicuous and unaffected. Taking in, therefore, all its merits, we can have no hesitation in pronouncing it to be by far the best book, in this department of natural knowledge, which is at present in the hands of the public.

ART.

ART. IX. Diary of a Journey into North Wales in the Year 1774, by Samuel Johnson, L. L. D. Edited, with illustrative Notes, by R. Duppa, L. L. B. Barrister at Law. 12mo. pp. 226. 9s. Jennings. 1816.

THE rich intellectual feast which Johnson had during his life time prepared for this age and nation, shall neither lose its charm nor fail in its attraction, till literature shall cease to delight the mind, or morality to enlarge the heart. One would have thought, however, that so splendid and so varied a banquet would have exhausted both the larder and the store-room of the provider; especially of one, who made every hint and every suggestion tell in the service of his table. Strange, however, to say, the obsequious Boswell, like an honest old housekeeper, partly from the purloinings of his master's pantry, and partly from the perquisites of his conversation, contrived so to enrich the poverty, and flavour the insipidity of his own calve's head, as to produce a very palatable and pleasant dish, from which every one, who can put up with the second table, may make a tolerable meal. We little thought that the keen and searching scent of Mr. Boswell, would have omitted a single scrap which could have added picquancy or substance to his olio; what the cook, however, had overlooked, the sagacity of the kitchen maid has discovered; for in an obscure corner, under the scullery dresser, Mr. Duppa has found the remnant of a bone, which, though it contains little enough upon it, is nevertheless dragged out in triumph, and having been washed and scowered, is immediately consigned to the Papins digester of a nine shilling duodecimo, flavoured with a peppercorn or two of Duppa and Piozzi, and is thus presented in due form to the public. Whether this precious relic had ever been examined by Boswell does not very clearly appear; but having seen the original MS. we are decidedly of opinion that it is in the hand-writing of Johnson. We shall now lay before our readers the manner in which it is presented to the public.

Contents of page 1.
July 5, Tuesday.

"We left Streatham 11 a. m.

"Price of horses 2s. a mile."

Contents of page 2.

"Barnet 1. 40'. p. m.

"On the road I read Tully's Epistles.

"At night at Dunstable.

"To Litchfield 83 miles,

"To the Swan,"

Contents

Mr. Newton's China."

Contents of page 6.

"8. To Mr. Newton's, to Mrs. Cobb's."
Contents of page 7.

"Dr. Darwin's. I went again to Mrs. Aston's, she
was very sorry to part."

Contents of page

8.

"9. Breakfasted at Mr. Garrick's. Visited Miss Vyse." Contents of page 9.

"Miss Seward. Went to Dr. Taylor's. I read a little on the road in Tully's Epistles and Martial."

Contents of page 10.

"Mart 8, lino for limo.

10. Morning at church. Company at dinner. "11. At Ilam. At Oakover. I was less pleased with

Ilam than when"

Contents of page 11. (in continuation.)

"I saw it first, but my friends were much delighted."

Such we would have our readers to know are the contents of the eleven first pages of this tour, as far as Dr. Johnson is coucerned. Three or four short notes inform us who was Mrs. Lucy Porter, who Mrs. Aston, and other personages of similar distinction, make up the due compliment of type, for of matter we cannot call it. In some pages farther on, the Doctor's journal becomes a matter of more general interest.

Contents of page 82.

"Two sheets of Hebrides came to me for correction to day." F. G.

"6. Zat. Sp. I corrected the two sheets. Myself last

66

night was disturbed.

Washing at Chester and here 5s. 1d."

We would fain know, Mr. Duppa, why the vouchers are not produced. We consider the absence of these as an instance of very culpable neglect on the part of the Editor. How is it possible that the public can form any fair opinion on the state of

Dr.