way would be a garden shed, for tools or other such things. The uprights should be formed of T iron (so called), which is rolled for boiler-making, iron boat-building, &c.; the roof of straw, hay, pease or bean stalk, or faggot, stacks, supported on light castings, made to fit the upper extremities of the T iron uprights, as in fig. 54.; and the lower extremities of the up

54

IT

rights either driven into blocks of wood sunk in the ground,

The circular form (fig. 57.) would be as easily built as a rectangular one, and would have great

stability. When only pease-straw, or other litter, was stacked,

56

pigs, calves, &c., might be kept in such structures without injuring them. The circular form would in this case be the best.

But a more perfect structure of this kind may be erected, having a permanent roof, yet capable of sustaining,

at any time, a stack of any kind; and I see no reason why all garden sheds, or even the buildings (or most of them) of a farmery, might not be thus flat-roofed, and so, in the latter case, answer the double purpose of buildings and rick-stands.

Supposing the walls constructed of cast-iron uprights secured firmly to foundation stones, and the intervals filled in any of the before-mentioned ways; the roof is to be constructed by laying light cast-iron beams or bearers, from one upright to another opposite it, and arching the interspaces with 4-inch arches. By these means the building will always be secured from the weather, whether the rick above be removed in part or not. Iron beams have hitherto been constructed generally from formulæ which make them much heavier than necessary. A late writer on this subject, Mr. Eaton Hodgskinson, has shown, and verified by experiment (vide Trans. Manchester Phil. Soc.), that, in place of the usual form and proportions of cast-iron beams, viz. the top and bottom ribs nearly alike in scantling, as in fig. 58., the bottom rib should be to the top rib in the ratio of 6 to 1; that the vertical or mid rib may be cast as thin as will insure a perfect casting; that the strength of such beams is inversely as the length, and directly as the depth, and not as the square of the depth, as hitherto supposed; and that the bottom rib should be formed into a parabola on its edges, terminating a few inches within the bearings.

58

I

The formula for the determination of the ultimate strength and scantling of such beams, given by Mr. Hodgskinson, is: cad ; where W is the breaking weight; a the area in

W =

square inches of the mid section of the bottom rib; d the depth of the beam there; 7 the length of the beam in inches; and c a constant quantity deduced from experiment, equal, for beams cast on their sides, to 24; and for those cast vertical, to 25.

The form, then, of these beams is somewhat as in fig. 59.;

59

a

in which a is the side view, b the cross section, and c the plan of the bottom rib.

I have particularly mentioned these beams, from their novelty of form, and their importance, as saving nearly one fourth part of iron; in other words, 75 tons of iron will bear as much in this form as 100 tons in the common ones.

Such beams, then, suited to the weight to be borne, and the length of the beam, &c., would support 4-inch brick arches; the haunches of which should not be filled up, but spandril walls built across, at certain intervals, level with the crowns of the arches, and there built open. Thus ventilation would be permitted between the rick and its support; and, when the roof was uncovered, would conduct the rain off.

Such arches should be turned in summer, and two or three coats of coal tar given to the extrados surface, by which they will be made watertight. I have constructed many such roofs as these, for various purposes, and they have been found to be light, cheap, strong, and staunch.

All buildings thus constructed would obviously be fireproof, and would last an indefinite length of time. The appearance of a tool-house so constructed will be as in fig. 60.

Sheds of this kind may be used for storing any garden or field produce, however damp: no matter what is stacked above, as no evaporation will permeate the roof.

The shorter the bearings of the beams of the roof (I call them beams, although, in most instances, they would be very slender), the greater will obviously be the saving of metal : for most purposes, 7 ft. or 8 ft. from post to post will be sufficient.

The appearance of such buildings might be much improved by a kind of cornice of two projecting courses of bricks round the tops of the walls. Corrugated iron might also be used for such flat roofs, arranged in ridges or arches from beam to beam; and the upper ribs of the beams might be hollowed to carry off the rain.

So much for these roofs and walls. All I have written

about them you will consider more as hints to work upon, than as any thing more valuable.

I am, Sir, yours, &c. 94. Capel Street, Dublin, Dec. 1832.

ROBERT MALLET.

SINCE we received the above communication, Mr. Mallet has sent us another (which we have forwarded to the Mechanics' Magazine); by which we find that, to his numerous other inventions, he has just added a most beautiful and most important one, viz. that of splitting all stones that can be separated into laminæ, by the application of male and female screws, instead of blasting, as heretofore, with gunpowder. The process is as follows:- Jumper holes are formed in the direction of the proposed fracture, as at present; but, instead of filling them with gunpowder, a split female screw is inserted in each hole, and the fracture is effected by the insertion of conical male screws. The success of this mode was proved before the Commissioners of Public Works at Dublin; and the advantages which would result from it, if it were generally adopted, are so great as scarcely to be foreseen. Not only all risk of accident from the blasts would be avoided, but the operation would be performed more cheaply, and, from its slowness, incomparably better. What can be clumsier than separating slate or other rock, for useful purposes, in such a manner as to reduce at least half of it to useless fragments? We congratulate our esteemed friend Mr. Mallet on his having made so important a discovery. We recommend our

readers to refer to the article, which will be found in the Mechanics' Magazine, vol. xviii.; and which will be read by all friends of humanity, and by all owners of quarries, and coal or other mines, with intense interest.

Cond.

ART. IX. Reply to some Remarks made by Mr. Main and the Conductor on Mr. Perkins's Mode of heating by hot Water. By A. M. PERKINS, Esq.

Sir,

I BEG, without preface, to answer your correspondent Mr. Main (p. 34.), by stating certain facts.

The first objection which I shall notice is, that, in consequence of the extreme smallness of the tubes, and very small quantity of water, the apparatus cannot have that equality of heat so desirable during night, when the fire is most likely to be neglected.

I shall answer this objection by referring to the specification of my patent, which describes a furnace of fire-brick, so constructed as to contain sufficient fuel for any specified time; and so capable of regulation, that the most equal temperature may be maintained for any number of hours required.

The apparatus which I first erected was at the villa of J. Horsley Palmer, Esq., at Fulham. This gentleman very liberally tried the first experiment on his own hot-house; and has, with equal liberality, allowed me to make use of his name to promote the spread of the invention. I therefore copy from his own memoranda, which he gave me at the time, a table that shows how completely the equality of heat was maintained in the hot-house for eight days and nights. A Sixe's differential thermometer was set at nine o'clock every night, and examined at nine o'clock the following morning; the fire was also made up, and not touched during the twelve The result was as follows:

hours.