inconsiderable in the case before us. Also the expression for the radius of curvature is in reality dependent on the varying ratio of the tension to the extension. But that the real deflection of a tube of the given dimensions, subject to the given weight, would be much larger than the deflection given in the published accounts, appears certain from this consideration: the strain would be more than 194 tons at the centre; and it would be larger for a considerable distance on either side the centre; consequently, the extension of the material would be great, and therefore the radius of curvature small, for a large portion of the curve; whereas the published deflection would make the radius everywhere large.

As it appears then from the evidence of practical men, and also from the computation above, that it is quite impossible that the tube could sustain anything like the computed tension, we are driven to the conclusion that the data themselves are erroneous.

We refrain from comment on this most disagreeable conclusion, for the charge which it involves is of too serious a nature to be disposed of satisfactorily in an incidental manner. The public were indubitably called upon to place confidence in the sufficiency in the tubular bridges by the evidence of this very experiment, of which the particulars, it is but too evident, have been wrongly stated. We are anxious to believe that the exaggeration of the strength of the model tube was unintentional, that it did not arise from an ignorance of the power of mathematics to detect the fallacy, or a futile hope to escape that irresistible cross-examination.

Happily we have the investigation of Mr. Hodgkinson to give confidence as to the strength of the actual Conway tube. Mr, Tate objects that whereas in the tubular bridge the upper side of the cells is more compressed than their lower part, that investigation proceeus on deductions from experiments in the direct longitudinal compression of cells by a pressure uniformly distributed over their ends. But the weight of the objection is small when it is considered that the inequality of the pressure is small on account of the comparatively great distance of the neutral axis, The general character of Mr. Hodgkinson's investigation appears to be that of a careful and moderate estimate of the strength of the Conway Bridge, which, if the complexity of the subject do not permit of its perfect accuracy, is far, very far, more worthy of confidence than any deductions from the Millwall "model tube."

Useful Hints on Ventilation. By W. WALKER, Engineer. Manchester: Parkes. 1850.

WE are glad to see from the numerous and cheap works which issue from the press, that ventilation is attracting its fair share of public attention, and we therefore welcome the present contribution, as no doubt our readers will; and although ventilation is now supposed to be well enough understood, they will no doubt read with satisfaction the extracts we here give, illustrative of Mr. Walker's practical treatment of the subject.

In reference to steam agency Mr. Walker observes:"However useful steam agency, as applied to ventilating purposes, may be in factories or buildings connected with them, and in theatres or other places liable to great and sudden influx or efflux of persons; and well as it has been found to answer in its application to other buildings, such as club-houses, banks, collegiate institutions, and hospitals, in which manifest advantages have been derived from its employment; there will still be great numbers and many classes of edifices in which it would be, from various causes, inadmissible. Churches, chapels, and houses for worship, may be enumerated under this head-the numbers contained within their walls being, on the whole, tolerably constant, and not liable to very sudden fluctuations; but especially from the circumstance that they are seldom used more than two days in the week, with intervals of two or three days between; and when used it is only for two hours consecutively, with intervals of two or three hours between. With such proper quantity and sizes of ingress and egress flues as can readily be obtained in the thick walls and piers of such edifices (if planned prior to their construction), this short period of occupation will not permit their atmosphere to become very highly charged with impurities, while the intervals between the services will be found sufficient for an entire change of the whole atmosphere left in them at the close of each service, without resorting to mechanical means. In churches with lofty open roofs, of the medieval or early-English construction, without galleries, the total cubic space bears so large a proportion to that portion of it occupied at the floor level by the congregation, that scarcely any injurious vitiation of the entire atmospheric contents can take

place during the short period of occupation, provided moderate preparations have been made for ingress and egress. Hence, very sudden and powerful ventilation is scarcely required in such ehurches, and the purification of their atmosphere may safely be left to the spontaneous action of those preparations; but on special occasions, and in hot weather, the action of the fresh-air flues may be accelerated by the exhausting power of a shaft or

trunk of adequate size running up within the tower or steeple, its upper end discharging into the external air, while its lower end communicates with the interior by openings in or near the roof; and this shaft may be made, in very hot weather, to perform two or three times its usual duty, by rarifaction produced at its lower end g by a large number of gas burners fixed there in tolerably close proximity with each other, and supplied with gas from the mains which furnish light to the whole building. These ideas have been successfully car

ried out in numerous instances and in large buildings. The whole process recommended for such a building will be better understood by a reference to the upper portion of figure 1, which represents a section of a church ventilated in this manner, a a, are openings all round the church for admission of fresh air; b b, hot-water pipes, over which it is made to pass on its way to the gratings c c; d d, are openings, by which the vitiated air enters a horizontal trunk e, from the end of which rises the shaft f, with a collection g, of gas-jets in the bottom of it; h i, is the gallery-line, and k, an excavated room for the boiler, the floor of which should be five feet below the floor-line of the church.

"By simply turning the cock in the gas pipe which supplies the jets, the rarefaction in the shaft, and, consequently, the velocity and quantity of the air passed through the church, may be controlled with tolerable accuracy, and instantly proportioned to any greater or smaller number of persons assembled. The cost of piping and cock for bringing the gas to the jets has been found to be but trifling; and as they need only be lighted during the time the church is occupied for worship, which is seldom of longer duration than two hours and a-half, the consumption of gas is not very great, and amply compensated by the beneficial result obtained.

"The means most proper to be adopted for the plentiful supply of fresh air in the low-roofed, galleried, and crowded meeting-house, will be found to consist in abundance of fresh-air openings all round under the windows, communicating by brick flues with the lower part of the spaces under the aisles and seats in which the hot-water pipes that are to warm the air should be fixed. Freshair flues should be constructed in all the piers between the windows, running as high as the gallery to supply it with fresh warmed air. A vitiated air-flue should also commence in each pier under the gallery (in order to give free egress to that which would otherwise be intercepted and detained under the gallery), and pass up into a horizontal trunk, running over the roof, along each side, into the foot of the upright shaft below the gas-jets, as before explained. Openings should also be left in the roof, communicating with these horizontal trunks, to carry off the bad and heated air over the galleries. Hot water pipes should be conveyed along the sidewalls, under the floor, so as to warm the air that passes up within the piers into the gallery.

"The leading points to be observed in such a case are delineated in the lower part of fig. 1, below the line h i.

"A much larger provision should be made for supplying fresh air

to such a house for worship, or other galleried building, than in one which has no gallery, and which possesses the advantage of an open roof; and those who would object to the copious measures here recommended, as unnecessary, should well consider the following facts and calculations. A chapel or meeting-house with large galleries nearly all round, capable of accommodating on special occasions 2000 persons, is frequently made about 75 feet square, and 25 feet average height, giving a total cubic content of rather more than 140,000 feet. Now the authorities, from Tredgold to Reid who have written on the subject of the quantity of fresh air, required per minute by each individual, to replace that which such individual has rendered unfit for respiration, vary in their conclusions from 3 to 10 cubic feet; and if seven cubic feet be assumed to be the proper quantity, an allowance near the average of their scientific opinions will be given. The total quantity required, therefore, on this low standard in such a building, to maintain its atmosphere in a state of purity when filled, will be (2000 x 7 =) 14,000 cubic feet every minute, and a like quantity of vitiated air must be carried off in the same time. The atmosphere of the building will therefore require to be completely changed or renewed (140,000 14,000 = 10) once in every ten minutes. Let it now be supposed that the unusual provision of 16 openings has been made all round the building, for fresh air, each opening measuring 18 inches by 6 inches. Deducting one-third of the area for impediment caused by gratings, will allow to each opening a clear area of Fig. 2.

half a superficial foot, and the aggregate area of all the openings will be eight feet. Now, to supply the required quantity of air (14,000 cubic feet) in the given time (one minute) through those openings, the air must pass through them all at the velocity of (14,000 8) 1750 feet per minute, or more than twenty miles per hour; which it will not do, especially on a calm day in hot weather, when ventilation is most needed, without the aid of some powerful stimulus; and if such artificial impulse be wanting, those openings will, under the circumstances, be quite insufficient to prevent the rapid deterioration of the atmosphere within, and ought, therefore, to be considerably enlarged. The bad effects of the usual way of obtaining a partial supply of air in such a case by opening the windows, have been already commented on.

"Take another example from a large Gothic church, with galleries, and lofty side aisles and nave, in the neighbourhood where this is written; measuring 80 feet by 65 feet, with a roof approaching to flatness, about 30 feet in average height. This church has often contained 1800 persons; its cubic contents being 156,000 feet, and the requirement of air, allowing, as before, seven feet per minute to each person (1800 x 7 =) 12,600 feet. The time in which the whole atmosphere of this church would, when containing its full complement of persons, require to be changed, is (156,000 required to pass the quantity in the time. 12,600) 12 minutes; and large openings will obviously be

These figures will suffice to show the necessity for a very much larger provision for ventilation than has been customary in buildings containing galleries, in which the cubic contents bear a small proportion to the numbers assembled."

"The management of the warming of a church being a matter frequently entrusted to a sexton or verger charged with other duties, which necessitate his making a clean appearance, and demand his exclusive attention during the service, it is a matter of some importance where hot-water apparatus are used, to adopt such form of boiler as will require the smallest possible attention. The kind shown in fig. 2 in the annexed section, will be found to fulfil this requirement; many large churches having been kept by it at a uniform temperature with only three attendances in twenty-four hours. This sort of boiler will be found very desirable in many other buildings besides churches. They are to be filled to the top with coke broken into small pieces, which falls on the fire as required. A very useful kind of Arnott stove has been largely adopted on the same principle."

The stove here described appears to us a very simple arrangement for effecting the purposes desired, and to be well worthy of adoption.

In the whole range of ventilation there is, perhaps, nothing so much neglected as the ventilation of schools; and as it is most desirable public attention should be turned to the subject, we most willingly give room to Mr. Walker's statement of his views on the subject:

"Schools are freqently very crowded, and their atmosphere in a most unwholesome condition. The great increase in their number in the populous manufacturing districts, is a gratifying sign of the times, and affords good reason to hope that the succeeding generation will grow up with improved ideas and habits, and, as is most needful in those districts, stand

瓜

a, Fire-box; b, Ash-box; c, Snoke-box; d, Fire-bars: e, Smoke-tubes; f. Fuel-box; g, Damper; h, Flow or steam-pipe; i, Return or condensation pipe; j, Ash-box door; k, Fire-door; 1, Smoke-pipe.

some degrees higher than their predecessors in the scale of civilisation.

"Fig. 3 is a section representing a boys and girls' school ventilated (except as regards the windows) in a satisfactory manner; a a are the fresh-air openings; bb, pipes for heating; cc, gratings for entrance of fresh warmed air; dd, openings for foul air, leading into a trunk e, whence it is drawn down the shaft ƒ by the rarifyingfurnace g, whence it is discharged up the shaft h into the atmosphere.

"This arrangement of a rarified shaft, continued down to the ground for the purpose of obtaining a quick draught by a heated column, and requiring a down shaft to connect the ventilating trunk, from the top of the building, with its lower end, so that the foul air may enter it below the fire, is the same that has been adopted, at very great cost, by Dr. Reid, in the new Houses of Parliament. There is a complexity and expense about this arrangement which would seem to be needless. The drawing down to the ground-level of the whole of the vitiated air of the building, and then sending it up again; the cost of connecting the main downshaft with the up-shaft, which circumstances may require to be at a considerable distance; and the trouble of forming air-tight connecting-flues to convey the vitiated air from numerous rooms to one main down-shaft, to say nothing of the double space and materials occupied by the two shafts, would render this plan, in numerous cases, impracticable. To overcome some of these difficulties, the fire has, in many cases, been provided for at the rooflevel (i fig. 3), thus relinquishing the down-shaft and the lower part of the up-shaft, and so far has been an improvement; but in many cases the trouble of carrying up fuel and ascending to attend to the fire was too great, and the ventilation was, therefore, uncertain. The best mode of effecting forcible ventilation by a shaft doubtless is, to adopt the last-named arrangement; substituting gas rarifiers for a furnace, as shown in the church. (Fig. 1.) By bringing the pipe which supplies gas to the burners to some accessible point near the ground-floor, with a stop-cock at that point, the handle of which should work in a graduated quadrant, the ventilation can be regulated from below with great precision. "Window-ventilation of a kind very frequently adopted in churches and schools, has been introduced into this figure (k fig. 3), not with a view to represent it as part of Dr. Reid's system, but to illustrate its bad effects, either where it is the sole provision made, or where it is used in combination with a better process. If it be the sole provision made, and the room be heated by a fireplace or stove, to 60°, a downward rush of air at 10° (should that low temperature happen to prevail outside at the time), will play upon the heads of those near it. If it be in force, as in the figure, simultaneously with proper means of introducing fresh warmed air, its force will be modified, and partially defected upwards, towards the egress openings; but whatever cold air thus enters, is so much deducted from that which ought to have entered warmed, through the proper channel c."

We may observe, that Mr. Walker has been largely engaged at Manchester in the construction and adaptation of stoves, and that he has had considerable experience in many practical applications of ventilation.

Suggestions for a New Street through the City of London, with a leading Aqueduct Sewer. By NATHANIEL BEARDMORE, M. Inst. C.E. London: Weale, 1850.

Mr. Beardmore proposes a very extensive system of street improvement and drainage. One part of his plan is to do away with Westminster and Charing-cross Bridges, and to construct a grand bridge leading from Charing-cross to the Waterloo-road. Another part is a street from Temple Bar, across Bridewell, south of St. Paul's Churchyard into Eastcheap, and thence by Crutchedfriars and Great Alie-street to the Commercial-road. Coupled with this, he proposes to carry a grand sewer through the metropolis, from Bayswater to Barking Creek.

Royal Agricultural Society's Prize Model Cottages. By HENRY GODDARD. London: Dean.

Mr. Goddard, an architect of Lincoln, gained the first prize for model cottages offered by the Royal Agricultural Society of England, and we presume that his designs were the best of those presented for competition; but we must say we have seen many designs which are more picturesque, and with better arrangements.

ON COOLING THE ATMOSPHERE OF ROOMS. SIR-I was very much pleased with the description given in your last number, of the very ingenious and simple machine for cooling the atmosphere of rooms. Among the many excellencies of the apparatus, not the least, I think, is the similarity between the means employed in it and the operations of nature constantly producing similar effects-I mean the change of temperature by change of density. It is, indeed, an extraordinary thought, that the changes of temperature observed at different heights in our atmosphere may be accounted for by the fact of rarified air having a capacity for heat, increasing with its rarifaction, and that the same air which, made dense by the pressure of the atmosphere, feels so warm at the surface of the ground, may, wafted to some hill top, and thus freed from some part of the pressure, become the cooling breeze; and anon, mounting still higher, may take its place among the regions of eternal snow. It appears to me that the similarity existing between the means employed in the apparatus, and this process in nature, forms the very best guarantee of its effecting the object desired in the most suitable manner, as the parallel between the two operations exists throughout.

It appears to me, however, that some explanation of the cause of the increase of the temperature of air on compression would render the account of the apparatus more intelligible to the general reader, as it might create misunderstanding on the subject merely to say that air increases in temperature on compression, and diminishes on expansion; the fact being, that on compression the same quantity of heat exists in the air as did before compression; but this increase of density diminishing its specific heat (i. e. the quantity of heat required to keep it at its former temperature), the amount of heat it possesses above this must make itself sensible, and raise the air to a higher temperature; while, on the other hand, when by being rarified, or being allowed to expand itself in a larger space, its specific heat being increased, the quantity it possesses is unable to maintain its temperature, and it consequently is diminished, though neither change of temperature is in the same ratio as the compression or expansion.

I should scarcely think it possible that the objection anticipated by the inventor-viz., that the cooled air would be found unpleasantly moist, could occur. For, supposing the air to be lowered to the required temperature, it would be able to hold in suspension an amount of moisture in accordance with its temperature; and, of course, any attempt at condensation of moisture must be made by removing some portion of the heat of the vapour. As Dr. Lardner, in his "Treatise on Heat,' observes (in speaking of the liquefaction of vapour by compression), that without an actual loss of heat having been sustained by the vapour, it would be impossible to imagine the condensation of any portion of the vapour into a liquid, as such condensation must be effected by the subtraction of all the latent heat which maintained the liquid in a vaporous form. But should it be found desirable to lower the temperature of the air more than could be effected (with air subjected to the amount of pressure stated as that best adapted to the purpose) by water of the temperature of 100°, or should it be found impossible to procure water of so low a temperature, I should think (as mechanical power must be used for condensing the air) that the mere evaporation of such water as can be procured-effected as described below, in a space approaching to a perfect vacuum in proportion to the degree of cold required, the vapour arising from the water being constantly removed, in order that its tension might not prevent the further evaporation of the liquid-would amply serve the purpose intended.

This effect might be obtained in the manner shown in the accompanying sketch, where A, B, C, D, is a cylinder, with openings at the sides to connect the pipes containing the air with the air chamber in the cylinder by spigot-and-faucet-joints. Water is to be placed in the cylinder, so as completely to cover the air chamber E, E, E, as shown by the level F, F. In the cylinder, a piston G works. This might be made perfectly air-tight with ordinary hemp packing, the upper plate of the piston being merely provided for the purpose of screwing down the hemp as might be found necessary, and being formed with large openings in it, as shown in the section; while in the lower plate a valve H, is placed, which might be loaded in a proportion relative to the tension of the vapour to be raised from the water. Thus, supposing the required temperature of the water to be 50°. The tension of the vapour of water at 50° is 0.375 of an inch of mercury; and as the amount of the pressure of the atmosphere (15 lb. on the square inch) is equivalent to 30 inches of mercury, it follows that the tension of the vapour of water at 50° is equal to an 80th part of the weight

of the atmosphere, which is equal to about three ounces. Now the valve in the piston being loaded in this proportion to its superficies that is, with a weight of nine ounces-if its superficies is three inches, and so on, it follows, that in the stroke of the piston the valve H would not be affected till the tension of the vapour became of the amount required, and, consequently, would not affect the temperature of the water till it was desirable to do so; and as the valve could be easily loaded with any weight, this would make the apparatus self-acting. The valve I, on the top of the cylinder, might be exactly balanced, so that there would be almost no pressure on the piston from the tension of the vapour above it: some lime also placed in a vessel on the piston would absorb the moisture remaining above it. The rapidity with which water loses its temperature in the exhausted receiver of an air-pump, shows that a few strokes of the piston would absorb enough of the heat of the water to lower it to the required temperature.

within them to rarify the air and cause it to ascend; but as in all these cases, the important object was trusted to the working of invisible draughts or currents which might not take place, and which very often, from unsuspected countervailing influences, did not take place aright, the object was most imperfectly accomplished. It was in the cotton-factories that fan-wheels were first set in motion, which, with a certain speed of evolution, were known to extract a certain quantity of air."-In this paragraph the merits of the respective methods are fairly stated, and the plan is also mentioned as simple, and certainly as effective as could be desired. In conclusion, I think that our best thanks are due to the ingenious and talented author of the apparatus under consideration for his very useful invention; the resemblance of the means employed, with the circumstance which, as he observes, is so often stumbled on by workmen, and is noticed in every work on natural philosophy, proves to us how long a principle may be patent to our senses ere our minds are struck by its applicability to purposes of general usefulness.

A

I am, &c.

Q.

F.

E

E

Ε

H

In the removal of the vitiated air, I cannot however but think that mechanical means would be far preferable to the mere opening of a sash, as this proceeding must cause a communication with the external air which would be far from desirable. And this circumstance at once brings under consideration the vexed subject of ventilation; that science so well understood in theory, but so lamentably displayed in practice, but which is at the same time a subject of so much importance, that I cannot refrain from quoting the words of a well known writer on this and similar topics. In contending for the superiority of ventilation effected by mechanical means, Dr. Arnott, in his Treatise on Warming and Ventilating,' observes, "It is a remarkable fact that the first accomplishment of perfect ventilation for a crowded place was not, as might have been anticipated, in the houses of the great and learned, and therefore in our houses of parliament or in the churches of the wealthy, or in fashionable assembly rooms of any kind—but in the cotton factories. In the first mentioned places it is true that openings were made in the ceilings and side walls, and cowls were placed over the openings or fires, or strong lamps were placed

THE ROUTE TO CALIFORNIA BY THE TEHUANTEPEC ISTHMUS.

MR. LETCHER, the American Minister at Mexico, it has been announced, has succeeded in effecting a treaty with the government of that country with respect to the Tehuantepec route across the Isthmus. It is understoodt hat this treaty is similar in its character and conditions to that recently made by our efficient chargé d' affairs, Mr. Squires, between our government and that of Nicaragua. The documents connected with the affair will soon be placed before the senate of the United States. The presumption is, that the stipulations do not vary widely from those incorporated in Santa Anna's decree of the 1st of March, 1842; and in that of Mariano de Salas, dated the 5th of November, 1846. The former decree contained eleven articles, and the third of the series declared that the passage across the Isthmus should be neutral and common to all nations at peace with Mexico. The government generally made this whole decree, upon certain terms, with Don Jose de Garay, who it appears, has surrendered in some way all the concessions orginally made to him to certain citizens of the United States residing at New Orleans. By way of distinction, therefore, this may be termed a New Orleans enterprise, though the results may be of national importance. The treaty was made on the 24th of last month, and it is calculated to call forth much discussion, as well as to excite great interest in every part of the country.

For many years the idea of making an easy route, either by railroad or canal between the Pacific and Atlantic Oceans, has not only arrested the attention of our countrymen, but the serious inquiry of several European governments. A ship railroad, with a capital of 10,000,0007. sterling, was proposed at one time in London, with a view of levying tolls upon all the nations of the earth. This was a gigantic scheme. When the mind contemplates the possibility of taking a ship into a dry dock on the Atlantic shore, of cradling it upon a car with 48 wheels, running upon eight rails, of seeing it transported across the country, and deposited in a dock upon the Pacific, the ingenuity of man becomes an object of admiration. We are startled with its boldness, though we can scarcely doubt the rationality of its recources. Vast capital can accomplish vast results. However, the English plan will not be carried into effect in the present century. The French and the Germans have made several surveys of different routes, as well as the English and Americans. That by Tehuantepec may or may not be practicable. Senor Gaetano Moro's survey gives a highly favourable picture of the country for the proposed road. From his surveys, it seems that the entire distance from sea to sea is 135 miles in a right line. It presents a wide plain from the mouth of the Coatzacoalcos to the foot of the Mesa de Tarifa, which is a table-land rising to 650 feet above the level of the sea, and at five miles distance decends again to the plain which reaches the Pacific. Near Tehuantepec, Moro found two extensive lakes, the outer separated by a narrow sandbank from the ocean, and the inner and larger communicating with it by a channel between high banks. Eight rivers flow into them, and, with some improving, ships may find harbours in these waters. From the inner lake the land rises very gradually to the Venta de Chicapa, thence with a steeper acclivity upon Tarifa,-and there is a slight declivity to a river, which is navigable for ships for the distance of 34 miles from its mouth on the Gulf of Mexico. Such are the rude outlines of Moro's survey.

The resources of the country are immense for timber of the best quality for building a road. The facilities for cattle-feeding are complete. The soil is prolific, and salt mines are abundant. The climate is agreeable and mild, and usually salubrious. The advantages, therefore, for constructing a road cannot be overlooked. In a commercial and political point of view, however, such a road would be very desirable; and, could it be made, would add largely to the prosperity of our country. From the mouth of the Mississippi to San Francisco, by Tehuantepec, is 1825 miles nearer than by Panama. From New York 1400 miles of sea navigation would be saved, were this route opened.

Fig. 2.-Transverse Section.

Fig. 3.-End Elevation.

30

40

50 FT

Fig. 1 represents the ground plan, which is 61 ft. 6 in. long, and 46 ft. 9 in. wide over walls. The circular tank is 33 feet diameter, and the centre part, which contains the soil for the plant, is 16 feet diameter. The eight tanks in the four angles are filled with aquatic plants of various kinds. The house is heated by a series of 4-inch cast-iron pipes all round the inside of the external walls, proceeding from a Burbage and Healey's boiler, and Sylvester furnace. The tanks are heated by 4-inch pipes underneath each, as shown in the section; and by smaller sized lead pipes resting on the paved ledge of circular tank, also shown in the section. There are 30 openings between the piers, all round the house, for ventilators. Different compartments of the roof are also made to open by simple machinery, for the purpose of ventilation. The pathways are raised 3 ft. 6 in. above the general level outside, and the roof is supported by light wrought-iron beams, resting on the eight internal columns, as shown on the ground plan.

Fig. 2 is a transverse section of the building, which shows a section of the circular tank, with the pipes under the centre part, and the small pipes on the paved ledge, forming the shallow part of the tank. Also the side pipes, and the manner of fix. ing the cast-iron columns; together with the construction of the roof and its gutters, facia board, &c. The wrought-iron beam shown in this section has a bearing in the middle, over the great tank, of 31 ft. 3 in. The height of the masonry, from the ground to the top of the coping, is 4 ft, 9 in.; the column and arch 10 ft. 6 in.; the plating and facia board 2 ft. 1 in., making the whole height from the ground line 27 ft. 4 in. By this section it will be seen that the upright sashes are placed behind the cast-iron columns.