1840.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



49 



WIRE FENCES. 



(From the Gardener's Magazine.) 



At an ordinary meeting of the Horticultural Society of London, tlie follow- 

 ing letter to the secretary from Mr. W. B. Booth, was read, upon the mode 

 of constructing wire fences for training espalier fruit trees upon, and for other 

 purposes. 



" CarcleWj January 29, 1839. 

 " S:r, I heg to hand you the following particulars respecting some wire 

 trellises lately erected here, which you may, probahly, not deem unworthy of 

 submitting to the notice of the Horticultural Society. 



" The object for which they are intended is the training of espalier fruit 

 trees ; and it occurred to me, in the course of erecting some wire fencing to 

 divide a portion of the park, that a similar kind of erection might be advan- 

 tageously introduced into the kitchen-garden, which would answer the same 

 piu-pose as the expensive wooden or cast-iron trellises usually met with in 

 those places where the espalier mode of training is adopted. I accordingly 

 submitted the plan to Sir Cliarlcs Lemon, who has since had it carried into 

 execution to a considerable extent. 



" Wire erections of the kind I am about to describe are not uncommon, I 

 believe, as fences, in some parts of the kingdom ; but in Cornwall it is only 

 within the last few years they have been introduced. Mr. Gilpin, in his ex- 

 cellent Hints on Landscape-Gardening, p. 217, has noticed the wire fence as 

 being best suited for those parts near to the house, or to the approach, but 

 he has not shown the manner in which it may be erected. The accompany- 

 ing sketches and details will, I trust, supply this deficiency, and enable any 

 one who may be desirous of erecting a wire fence or trellis to do so, with the 

 assistance of a mason and blacksmith, at a very moderate expense. The wire 

 used is known as No. 32. It is about a quarter of an inch in diameter, and is put 

 up in large coils. Each wire measures from 115 ft. to 120 ft. in lengtli. The 

 main upright posts fig. 153 a a are of iron, 1^ in. squax'e, and from 5^ ft. to 

 6 ft. high, with holes 6 or 7 inches apart for receiving the small screws and 

 nuts, to which the wires are attached in the way shown at fig. 152. At the 

 opposite end the wire is secured by being bent a little at the point, and having 

 a small wedge driven over it in each of the holes of the upright. Both tliese 

 main posts are i\ ft. above the level of the ground, and are fixed beneath the 

 surface in large rough blocks of stone d e, with iron wedges, which are more 

 convenient, and answer the purpose quite as well as if they were run in with 

 lead. The stay-bar is round, and 1^ in. in diameter. It varies in length ac- 

 cording to the inclination of the ground, but when the latter is nearly level 

 it is about 7 ft. long. The up|ier end is flattened, and beveled, so as to 

 square with the upright, to which it is fixed by means of a screw at,/". The 

 lower end is only a little bent, that it may fit into a somewhat smaller lilock 

 of stone e than the one at d. The connecting bar c is square or round, and 

 need not exceed an inch in either ease. It will also vary in length, accord- 

 ing to circiunstanees. On a nearly level surface it must be about 5 ft. long, 

 and have an eye at each end large enough for the end o€ the post and stay to 

 go through. In addition to this, there are uprights of one-inch flat bar by 

 half an inch in thickness fixed in stone, at 30 or 40 ft. apart, or even nearer 

 if necessary, for the purpose of stifl%ning the trellis. 



" In the erection of this kind of trellis, it is requisite to have an instrument 

 for drawing the wires Uke the one represented at fig. 151 to the scale of an 

 inch to a foot, wliich may be made without much difficulty. The one 1 have 

 sketched was constructed by our own blacksmith, and is a very eflicient con- 

 trivance for the purpose. After the stones are bored and set in their places, 

 with the earth firmly rammed around them, the next thing to be done is to 

 fix the main post a, and wedge it tight. It ought to lean about an inch back 

 from the perpendicular, to allow for its giving a little when the whole strain 

 of the wires comes upon it, which will bring it upright. The connecting bar 

 c is then slipped down over it, wliile the lower end of the stay-bar b is put 

 through the other eye and into the stone e, and the upper end screwed to the 

 main post at/. The triangle from which the wires are to be stretched is then 

 complete. A similar triangle must be made at the opposite end, and against 

 the main post of which p the instrument above noticed is to be placed for the 

 pm-pose of drawing the wire. This is done with great facility by means of a 

 double piece of rope-yarn twisted several times round the end of each, and 

 hooked, as shown at h. The screw g is then worked until the wire enters its 

 proper hole in the post^, when it is bent and secured by a wedge, as already 



stated. The nuts on the bolts fig. 152, at the end from which the wires were 

 drawn, are then screwed up a little, so as to make all tlie wires as tight as 

 possible. The cost of the whole averages from Is. (>d. to 2s. per yard. 



" I have been thus minute with the details of the trellis and the mode of 

 erecting it, in order that those who approve of it may be al)le to have others 

 erected on the same plan, for either of the purposes to which it has been 

 successfully applied at Carelew. 



" I am. Sir, your very obedient servant, 



" Wm. B. Booth." 



STEAM BOAT PROPELLERS. 



Sip, — Whatever effect tlie experiments of Geo. Rennie, Esq., on 

 steam-boat propellers, may have on the public generally, allow me to 

 say, that I consider conclusions more erroneous were never before 

 formed from any experiments, and with your permission I will attempt 

 to prove, that the assertions relative to the superiority of the spear- 

 shaped paildles are utterly without foundation. And what are these 

 assertions, and what are we called on to believe? Why, that the 

 floats of a paddle-wheel, when made in the shape of a trapezium, 

 (with tlie acute ends down,) present double the resistance to the com- 

 mon rectangular floats with three times the width and equal area! 

 A most important discovery certainly ; and pray how is it that all our 

 writers and experimenters on practical hydraulics have neglected to 

 make known to us this peculiar but important property of the trape- 

 zium ? Is it not for this simpk' reason, and this only, that they never 

 could have discovered that such a property belonged to it? Indeed, 

 it is a most glaring inconsistency to imagine that a flat surface, 

 fashioned into a trapezium, can present double |the resistance to a 

 rectangular s\wface of equal area : we say that there is no authority 

 whatever for the assertion, and happily for us Mr. Rennie has placed 

 the proof within our reach. 



We find, in the second table of experiments, (p. 25 of the Journal,) 

 that a paddle-wheel of 3 ft. 3 in. diameter, with rectangular floats 

 '••4x4 in., the total area of floats immersed being 22S-8 sq. in., pro- 

 pelled the boat at the rate of 2'S miles per hour, with -11-S revolutions 

 of the winch per minute. Also, that with trapezium-shaped floats, 

 ^4x4 in. (the acute ends down,) and immersed area 1ij7 sq. in., with 

 a wheel 3 ft. lo| diameter, and 47'.5 revolutions per minute, the same 

 boat was propelled at the rate of 2-0 miles per hour. 



In the first case, i. e. with rectangular floats, we shall find on calcu- 

 lation, that the centre of pressure, (assuming it in each case to be the 

 centre of the floats,) travels at tlie rate of 3s2'0 ft. per minute, or 4-35 

 miles per hour, and the velocity of the boat is stated to be 2-8 miles 

 per hour; the diflerence between these two quantities (4-35 — 2-y) = 

 1-5.5 miles per hour : this is the rate at wdiicli the floats, with an area 

 of 228'S sq. in. recede in the water, to obtain resistance sufficient to 

 propel the boat at the rate of 2-8 miles per hour. 



In tlie other case, i. e. with trapezium-shaped floats, we sliall find, 

 in the same way, that the centre of pressure travels at the rate of 

 4(i(;%3 ft. per minute, or 5*3 miles per hour, and tlie velocity of the 

 boat being only 2-'J miles per hour, shows that the floats, having an 

 area of 1U7 sq. in., recede at the rate of 2'4 miles per hour, to produce 

 an equal resistance, (or nearly so) to the rectangular floats. 



A writer in that excellent and useful publication, the Mechanic's 

 Magazine, states the propeller to be "an important modification of the 

 old paddle, being an ingenious application of a most simple and beau- 

 tiful principle in nature," and mentions also the observation of the 

 talented inventor, Mr. Rennie, " that nature never attains her ends but 

 by the best and most efficacious means," meaning, of course, that the 

 propeller in question is "the best and most etHcacious." As Mr. 

 Rennie seems to have followed nature so closely in his invention, it 

 seems passing strange that he should have overlooked another of her 

 principles, equally simple and important, viz. that of the resistance 

 opposed to the motion of a body through mater being as the square of the 

 rtlocity : had he tested the perfonuLuice of his floats by this simple 

 law, he would have seen at once on which side the efficiency rested. 



With the rectangular floats, we have seen that the recession, or the 

 velocity of the floats through the water, is 1-55 miles per hour; the 

 square of this is 1-55 x 1'55 = 2 4025. 



The recession of the trapezium-shaped floats is also shown to be 

 2-4 miles per hour, the square of which is 2*4 x2'4^ 5'7G. 



The area of the immersed floats necessary to produce an equal 

 resistance in each case, is of course inversely as their velocity; 

 and taking the area of the rectangular floats moving through the water 

 at the rate of 1-55 miles per hour, at 229 sq. in., we find, by simple 



