this state be polished, we observe that its surface undergoes various changes of colour; first it becomes pale yellow; then bright yellow; then reddish brown; then blueish, and light blue, then full blue; and lastly purple and black. The cause of this change in the hardness of the steel is referable to change of texture; and the great alteration it suffers has been rendered curiously evident by Mr. Daniell. A bar of steel was broken in two and heated red; one part suffered to cool spontaneously, the other quenched in water. The former was easily acted upon by muriatic acid, the latter with much greater difficulty. The former had a fibrous and wavy texture; the latter was like worm-eaten wood, compact, and not striated.

In noticing the singular properties exhibited by different kinds of steel and iron, Mr. Brande mentioned the mode of imitating Damascus sword blades, and the manufacture of stub iron.

Tin is a metal, the mineralogical history of which is extremely simple, for there is only one ore, which is the native oxide, or tin stone. It is found crystallized in octoedra and in four-sided prisms, resulting from their elongation. It often presents curious macles, or twin crystals. A ferruginous Those who variety of oxide of tin forms the wood tin ore. are curious in regard to the history of this ore, I must refer to a valuable dissertation upon it by Mr. Phillips, in Vol. II, of the Geol. Trans.

Tin, geologically speaking, is an old metal; its veins are cut by those of copper. Cornwall may be considered as the richest tin district in the world. It traverses granite and slate, accompanied by quartz, &c. Sometimes immense masses of the ore have been raised, and it is curious that particular varieties of crystallisation belong to particular mines. Thus Penandrae near Redruth abounds in twin crystals; PolgarthHuel Fanny, and other mines, are renowned for particular crystalline forms. The ores are reduced by simple ignition with charcoal.

Pure tin approaches silver in appearance. Its specific It is malleable and melts at 448° Fahrenheit. gravity is 7,9.

There are two oxides of tin, the gray and the white. The former contains, 100 + 14 oxygen; the latter, 100 + 28. These oxides are soluble in fixed alkalies. Tin is not easily oxidized by air and moisture; hence tin plate, which is an alloy of iron and tin, is much more durable than iron.

The two oxides combine with acids; the salts containing the protoxide have a strong attraction for oxygen; and hence precipitate many of the metals in a metallic state, or otherwise rob them of oxygen. Nitromuriate of tin is used by dyers of scarlet.

ART. XIII. On the Ventilation of Covent Garden Theatre. On a former occasion (Vol. IV. p. 383) we adverted to the

ingenious and effectual manner in which the ventilation of Covent Garden Theatre has been effected. At the desire of many of our readers, we applied to Mr. Harris for permission to examine the various contrivances, and to inquire into their efficacy, which was most liberally granted; and we are indebted to the Marquis de Chabannes, under whose directions the ventilation has been perfected, for the description and plates annexed.

We have before stated, that the principle of ventilating and regulating the temperature of this large building depends upon the constant admission of fresh air into the lower parts of the theatre, cold or warm, as the season requires, while the heated and foul air is continually carried off by tubes connected with heated cylinders. The gas lights are well contrived, so as to co-operate in this ventilation, and thus, while the house is admirably lighted, the whole of the burned air is conducted away, and none of that closeness and suffocating sensation is perceived which common lamps are apt to produce, and which is more especially occasioned by ill-devised gas illumination.

The following description of the plates will sufficiently explain the most important parts of the apparatus by which the temperature of the building is regulated, and by which a

constant renovation of the air is effected. Those who are inquisitive, will find thermometers in different parts of the theatre, which amply demonstrate the efficacy of the plan. In winter they are kept up at 60°, and in the warm weather seldom exceed the external temperature more than a few degrees, an advantage of which no other theatre can boast.

Plate VI. represents a ground plan and section of Covent Garden Theatre.

a. The stage.

b. The audience.

Description of the Ground Plan.

c. A stove at the Bow-street entrance. It was necessary to give great power to this furnace, that from the warm air mixing with the external air admitted by the swing doors, the temperature of the grand staircase might be always maintained from 55 to 60 degrees, whatever might be the cold on the outside of the building. On the power of this furnace depends, in a great measure, the temperature of the corridores.

d. Shakspeare's room. This being a waiting room not only for the half-price visitors, but also for the public in going out while waiting for their carriages, it was essential to place two stoves, as at f, which producing three times more heat than a common stove, might maintain the corridores at 60, independent of the furnace, which must cease to be lighted when the thermometer is above 50 out of doors,

e. Piazza entrance. A furnace is placed below this entrance, and the warm air is thrown out at each side of the flight of steps, by which means the air, which enters the body of the house through the doors above, is always at from 55 to 60 degrees.

f. Stoves in the lower saloon, and in the corridore of the dress circle on the King's side, as well as in the saloon and corridores above, not seen in the plate, which diffusing a large quantity of warm air, are of great benefit in pre

1

venting any current of cold air between the boxes and corridores. They are more particularly required the days in which the furnace below is not lighted, in order to maintain a proper temperature in the corridores, by which, instead of feeling chilly in passing through them, one is, in every part, as comfortable as if in a moderate sized apartment.

g. A furnace is placed underneath to warm this staircase, which leads to the private boxes on this side of the house, and one issue of hot air is also thrown into the private staircase leading to his Royal Highness the Prince Regent's box. The private box staircase on the other side being on a much smaller scale, a stove has merely been placed below to temper the air from the exterior. h. A very powerful furnace is erected under the pit entrance, and the warm air is thrown up in three places, which are not marked in the plate, being under the boxes. The most powerful heat is in the centre of the corridore round the pit, and at this entrance outside the swing doors which are entirely open to the external air, but for the powerful heat issuing immediately between the 1st and 2nd swing doors, the rush of air would be very dangerous. Thus the rush, which is admitted into the pit and body of the house by the centre 2nd swing door, is always at a temperate degree, and does away with the draught which formerly used to be complained of by persons in the front of the dress circle every time they were opened, and which would now be doubly injurious from the very powerful ventilation. The other heats are at the side doors into the pit, and have the same effect there, as well as preventing the cold from annoying persons seated in the front benches of the pit, by rushing to their legs and feet. It is further proper that the air in this corridore should be at 60 degrees, as it is from hence principally that air is supplied to the interior of the boxes-blaze openings communicate with the passage between the basket and dress circle immediately above, as at i, and

would be dangerous and unpleasant if the temperature of the corridore, from whence it is taken, was not kept at an equal degree to those above.

i. Openings to admit fresh air in the corridore between the basket and dress circle.

k. Two double wooden trunks, to supply fresh air to the first and second tier.

1. Forty-four steam cylinders placed round the mazarine floor

underneath the stage, and supplied by a steam boiler. m. Corridores running between the dressing rooms and stage,

and warmed by the furnaces at each staircase entrance n. n. Two staircases leading to the stage and all the upper dressing rooms, Two powerful furnaces are erected underneath, and the warm air discharged immediately in the centre of each, preventing any cold air rushing to the stage, and warming all the communications to it.

Description of the Section of Covent Garden Theatre.

a. The stage.

b. The audience.

c. Ventilating furnace erected in the lower gallery, of which a minute description is given in plate VII. and which draws the vitiated air from the basket and different tiers of boxes by conductors d.

d. Conductors for impure air from the different boxes to the recipient of the ventilating furnace.

e. Th`rd tube. A tube surrounding that which carries off the smoke and air from the furnace, and by the heat of the inner tube causing a rarefaction, which draws off part of the air from the back of each gallery, and discharges it through the cowl.

f. Ventilation by heat from the chandelier.

g. Ventilation over the stage to carry off any smell from the lamps, and all smoke made on the stage.

h. Tube in which the power to effect the ventilation is placed. i. Machines for lowering drop scenes.