]846.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



319 



openings then demanded by the growing fashion of fenestral decoration ; as 

 Chaucer says, 



richly peint 

 With lives of many divers seiut. 

 He ahandoned the high-pitched shingle roofs, excluding sun and air, and 

 was one of the first to employ the low pediment, and roof covered with 

 lead; and in his works we first discover the liammer-bearu roof in all its va- 

 rieties — -a system of the highest ingenuity and constructive economy, hotli 

 for space and material, as well as beauty and power, as exhibited in West- 

 minster Hall, Elthara Palace, Windsor Hall, and our college chapels and 

 halls. 



BARKER'S MILL. 



Sir — Perhaps through your valuable journal you would be kind enough to 

 decide the following argument : — Doctor Barker's Mill. One gentleman 

 argues " that the power is obtained by the resistance of the atmosphere to 

 the egress of the water, thereby causing a reaction." 



The other gentleman denies such to be the cause, and says, " that it 

 would revolve with greater power if placed in vacuum." Leaving it for you 

 to decide, with many apologies. I remain, Sir, your obedient servant, 



A Constant Reader. 



In Barker's Mill the supply of water is obtained from a cistern placed at a 

 considcraliln height above the revolving tubes or arms, which, if the orifices 

 of them were stopped, would sustain a hydrostatic pressure acting equally in 

 all directions, and proportioned to the depth below the surface of the water 

 in the reservoir. When, however, the orifices are opened, there is, ii. "ach 

 revolving tube, a predominating pressure on one side of it ; for it is clear 

 that the internal area of one side of the tube exceeds that of the other 

 sides by a quantity equal to the area of toe orifice. 



The motion is in the direction of that side of the tube which sustains the 

 greatest pressure. The external air is a cause rather of retardation than ac- 

 celeration, on account of its resistance to each arm on the side opposite to 

 the orifice. It may be easily conceived that if the atmospheric pressure 

 accelerated the motion, an increase of that pressure would increase the ac- 

 celerating force. If this view were correct, the arms ought to revolve more 

 rapidly if immersed in mercury, which certainly would not be the case. 



Very similar to Barker's mill in its mode of action is the rocket used in 

 pyrotechny and for military purposes. Here the iguited powder generates 

 an elastic gas, which presses on one end of the chamber containing it, hut 

 escapes bythe open end ; the motion is, of course, in the direction of the 

 end subjected to the elastic pressure. The external air tends to retard the 

 escape of the gas, and, to a certain extent, increases its pressure by partially 

 confining it ; but the accelerating force so gained is far more than compen- 

 sated for by the resistance which the air acting on the external surface of 

 the rocket offers to the motion — a resistance varying nearly in the square of 

 the velocity. 



The revolving steam-machine of Hero, of Alexandria, is another instance 

 of the application of the same mechanical principles as those of Barker's 

 Mill. 



The apology with which our correspondent concludes his note is quite 

 unnecessary ; we know no better way of serving the interests of our sub- 

 scribers than by considering questions like the present as they arise, and con- 

 tributing as far as we can to the solution of them. 



ST. MICHAEL HEAVITREE. 



Mr. Editor — In this month's Journal, at p. 291, under the head of St. 

 Michael Heavitree, is a small paragraph relative to the new church there, 

 which was designed by me, and executed under my sole superiulendance. 

 The paragraph is altogether erroneous ; and how it could have crept inlo 

 your paper, generally so accurate, I am a loss to ihink. Who Mr. Alex- 

 ander is I cannot think, no such a person was ever in any way connected 

 with the matter. Will you please in your next number to correct this. If 

 you can find, next mouth, space for a few concise particulars relative to 

 the church, which is a large one, and esteemed highly in this city, yuu 

 would oblige, and I would with pleasure send them. 



Your very faithful Servant, 



David Mackintosh, .Architect. 



Exeter, Sept. 2, 184G. 



For the following additional particulars we are indebted to Mr. Mack- 

 intosh, who has forwarded them at our request: — 



This church has been rebuilt on an extensive scale, and in a most sub- 

 stantial and perniaDent manner. The style is that of the Fifteenth Century, 

 and all the peculiar characteristics of the ancient church (a small edifice 

 of early perpendicular date) have been carefully maintained and restored. 

 The dimensions wiihin the walls are as follows:— chancel 23 ft. G in. by 

 16ft.; nave 86 fi. by 22 ft. ; north and south aisles each 94ft. by 13 ft. 

 Gin., with a southern porch in the second bay from the west end. The 

 height from the stone flooring to the summit of the open roof internally is 



44 ft. 6 in. The vestry is placed at the eastern end of the north aisle; ex- 

 ternally the walls above the plinth are built with lime stone of a blue grey 

 lint, from Chudleigh, and the windows, string courses, battlement, mould- 

 ings, and other dressings are of Caen stone. The plinth is of granite ; the 

 walls 3 ft. in thickness, and the gables are surmounted by floriated crosses 

 of rich character. The church internally is remarkable for the high pitch 

 of its fine open roof, consisting of 13 pair of grained principals with cir- 

 cular ribs of oak, wrought and moulded, and enriched with carved bosses 

 coloured and gilt after ancient ones in tiw. old church ; the principals spring 

 fnai richly carved stone tubals, and the columns and arches separating 

 the nave from the ailes, are a restoration in every point as regards detail 

 of those in the old church. They are especially rich and varied in their 

 foliage and capitals, and are carved with muib spirit and vigour illus- 

 trations of these capitals are intended to be published by the Exeter Archi- 

 teclural Society in their transactions. There is a fine chancel arch, richlv 

 moulded in Caen stone, on the north side of which is placed Ihe pulpit 

 hexagonel in form, and an elabonite specimen of stone carving, executed by 

 Rowe, of Exeter; it abounds in rich foliage, varied in eai:h compartment, 

 and carved in bold relief, having niches surmounted by crocketted canopies 

 over figures of the four Evangelists and St. Michael the Archangel. There 

 is a fine eagle carved in old oak, and an open Litany desk. The eagle was 

 carved by Mr. Winsor, who is the senior verger of Exeter Cathedral. All 

 the carved works in this edifice are admirably executed, and prove the 

 great advance lately made in Ihe correct execution of wood and stone 

 carving. At the east end of the chancel it was at first intended to have 

 restored the former window, but on inspection, being found much decayed, 

 as well as of a somewhat debased archilectural characler. The Rev. Dr. 

 Warren, of Portview, liberally presented a new window of fourlighls, and 

 the Rev. Arthur Atberley (the Vicar) has munificiently filled the same with 

 stained glass at his own expense. The design of this glass, which has 

 been executed in a most satisfactory manner by Mr. Robert Beer, of Exeter, 

 a talented and rising artist, comprises figures of the four Evangelists under 

 storied canopies having scrolls at their feet, on which are texts having 

 reference lo the Supper of our Lord. In the upper tracery are placed the 

 Phoenix and Pelican; the Symbols of the Evangelists; the Virgin and 

 Infant Jesus ; and St. Michael (the patron Saint of the Church) in conflict 

 with the Dragon. The south window of the chancel has a fine figure of 

 the Virgin bearing in her hand her emblem, the Lily, lu the south aisle 

 there is a good specimen of a memorial window of three lights. The first 

 and third are bordered after a specimen in Exeter Cathedral, in a flowing 

 pattern and blue glass, with the "Crown" quaiTy within, the centre bor- 

 dered in ruby glass with the " Trinity flower" quarry, the family arms, 

 and badge of the order of the Bath being inserted. At the bottom of the 

 window the names of the father and his two sons, buried in the adjoining 

 church yard are recorded, and the scripture '■ blessed are the dead which 

 die in the Lord" runs through the lights. The font is the gift to the church 

 by an old parishioner ; it is of Caen stone, large, aud highly enriched ; it 

 is placed near the western entrance. The bowl is octagonal, having each 

 panel filled with ornamental tracery, varied in each compart:nent ; the 

 sides of the shaft are likewise panelled with cinque foil headed arches, 

 aud springing from the shaft to support the bowl, are a band of angels with 

 expanded wings, bearing shields. For the present the old tower still re- 

 mains, but it is hoped, ere long, to add an adequate tower and spire, which 

 when complete, will render this one of the largest and finest churches in 

 the county of Devon. The contracter for Ihe whole of the works was Mr. 

 John Henshole, of Heavitree, v\ho has fulfilled all his ohligalions in the 

 most satisfactory manner. The works have been well done and unworthy 

 imitations avoided. 



DIFFERENTIAL HYDRAULIC PRESS. 

 I think it must be evident to all who have thought on the subject, how 

 much superior the Hydraulic Press is to the Screw, where enormous pressure 

 is required ; but even in the hydraulic press, as at present made, if we wish 

 to increase its power to a great extent there appears but three ways of ac- 

 complishing it, all of which are liable to objection: the first plan is to in- 

 crease the size of the large piston and cylinder, thus making it more expen- 

 sive and unwieldy ; the second is by diminishing the size of the smaller pis- 

 ton, but if this is carried too far it will be in danger of bending or breaking 

 under the pressure which is applied to it ; the third is to obtain greater 

 leverage upon the small piston, which if carried too far will also be in danger 

 of injuring it. But it appears to nie that it is possible to diminish the acting 

 part of the piston to almost any extent, wliile its strength remains the same 

 by the plan which is given in the figure, in which i is the large piston work. 

 ing in the stufiing box c, and carrying the press-board v upon it ; d e'u the 

 small piston or forcing pump thicker at the part d, than at e, and works in 

 the two stufiing bo,xes/ and g-, and is nearly at the top of its stroke. A is 

 the pump cylinder communicating with a reservoir in this cylinder, the small 

 piston works, descending through a water-tiglit collar into the space s, which 

 is open to the air. A: is a pipe communicating with the large cyander at the 



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