354 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



[October, 



qualities at cither end being equalized by the eye — and the distance 1 

 noted. Tins first distance is brought forward at the second division, j 

 and the sum of the first and second at the third, and so on; thus, if i 

 the length of the first division is five chains, the scale, when applied ! 

 to the second, is set on the left han 1 at five chains; and if the second 

 division is seven chains in length, the right hand extremity is set to 

 twelve chains, which quantity is again brought forward at the third 

 division, and so on until the whole distance of a field, in strips of one I 



chain, is ascertained, when the acreage is at once deduced, by cutting 

 off three figures from the right hand — those on the left are acres — 

 whicli are multi|)lied for roods and ])erclies. An ingenious application 

 of the above system is now in operation at the Tithe UHice, by which 

 means all calculation is avoided, and the area has merely to be read 

 off on a scale. The following diagram and explanation will enable 

 any surveyor instantly to practice it : 



„10 „9 ^9 ,9 „9 38 ,8 ,8 „8 ,7 .7 J „7 36 „6 ,G „6 ^5 „5 ,5 „5 



"The instrument consists of a box rule, with divisions at ii chains 

 apart, and numbered U,„0,,&c. ; at four of these divisions, or ten 

 chains, it is numbered 1„, or an acre — the reader bearing in mind that 

 the divisions, on the tracing paper laid over the field to be computed, 

 are one chain apart — therefore each single division, as 0,, is a rood. 

 There is a brass slider attached to the rule with a horsehair strained 

 perdendicular to its length, for the purpose of equalizing the fences 

 at the end of eacli strip. On this slider — which embraces rather more 

 than two roods in its aperture — are laid off 40 divisions, on alternate 

 sides, each way from tlie centre, and which are exactly the length of 

 one rood, consequently each division is a perch The figures on the 

 upper side denote the acres and roods, as far as the rule extends, and 

 are continued backwards on the lower part; the large figures are acres, 

 and the small figures roods. Now, to apply this instrument to prac- 

 tice, lav the ruled tracing paper over the enclosure, and move the 

 slider until its centre is on U„; place the scale in such a position that 

 the horse-hair forms a mean line of such part of the left hand bound- 

 ing fence as is included in the first strip of one chain wide, and press 

 it gentlv on the paper ; with the right hand move the slider along 

 the rule, until the horsehair forms a mean line on the required part of 

 the right hand bounding fence. Then move the instrument a/ZojjtMtT 

 on to the next division — the slider still remaining as last set — the 

 horsehair forming a mean line, as before, w ith the left hand hedge ; 

 press the ru'e gently, and move the slider on the scale, until the horse- 

 hair forms a mean line with the right hand hedge, as before ; which 

 process is repeated until the entire length of the rule is passed over, 

 when it is reversed, and the slider moved towards the left hand, the 

 equalization in this case commencing first on the right hand side. 

 When the slider is brought back to its original starting point, if there 

 remains any further quantity, it is again moved forward to the right, 

 as at first, the continuous measurement being easily kept up by the 

 decimal arrangement of the contents. For example, in the position 

 (he slider occupies in the diagram — supposing it had been moved over 

 the scale and back- — the contents woulii be ten acres and 3 roods; and 

 if, instead ot the centre exactly coinciding with the division repre- 

 senting 3 roods, it was '20 of the small divisions on the slider beyond 

 it, the contents would be 10 acres, 3 roods, and 20 perches. As a 

 proof of the great saving effected by this instrument, we need only 

 observe, that the price of scaling' has been reduced from 50 to 75 per 

 cent, since its introduction." 



In our last number we stated that in this work, there would be found 

 several useful hints, we shall therefore conclude by giving another ex- 

 tract, although it may not be new to the experienced practitioner, we 

 have no doubt it will be found serviceable to the student. 



"On the subject cf reducing and copying plans we cannot be ex- 

 jiected to say much. For ordinary purposes the pentagiaph presents the 

 readiest method, both for copying on the original scale, and also for 

 reducing or enlarging the copy to any proportional size of the original. 

 There are, however, several improved instruments for copying with 

 greater accuracy than the common pentagraph admits of. llie re- 

 ducing of a jilan by hand, is commonly performed by drawing squares 

 of a size commensurate with its minutiae all over its extent. .Similar 

 squares of ary required proportion to the first are then drawn on the 

 paper on which the plan is to be copied, and in every square of the 

 copy is constructed that which is contained in the corresponding 

 square of the original ; to enlarge a plan the operation is reversed. 



"A much more accurate method than the above for reducing or en- 

 larging plans for railways or other similar purposes, is, to lay down 

 lines of construction thereon, in precisely the same manner as would 

 be done in surveying it; then take ofl' the lengths, offsets, &c., viith 

 the proper scale, and replot the survey to that scale on which it is 

 required. The usual method of copying plans by hand is to piick all 

 the angular points and principal features through the original on to a 

 plain sheet of paper fixed beneath it, ou which the copy is to be drawn; 



these points being then connected — first with pencil lines — are inked 

 in, and a tolerably accurate copy obtained: but the method is not to 

 be recommended, from the injury it does to the original, and the inci- 

 dental errors from oblique punctures of the pricker, &c. The best 

 method of copying plans, which we are aware of, is either by a copy- 

 ing glass, or by tracing and transferring. That by the copying-glass 

 is performed thus : — in a frame, which can be fixed at any inclination, 

 is placed a sheet of plate glass; to the. frame is fixed the original 

 plan, and above it the paper on to which it is to be copied; the frame 

 is then placed behind a strong light — or lighted candles placed below 

 it — which enables the draughtsman to see all the lines of the original, 

 and to trace them in ink on the plain paper without difficulty.* The 

 second method is to make a tracing of the original on proper tracing 

 paper; rub the back of it with powdered black lead, and fix it down 

 carefully on to the paper on which the cooy is to be made; then 

 lightly trace all the lines with the end of a porcupine's quill, or other 

 pointer which will trace fine lines, and a perfect copy similar to pencil 

 will be obtained, which has then to be inked in." 



We again with much pleasure recommend this work to the student, 

 we think it the best practicable work that has been published on land 

 surveying. 



ON THE ORIGIN OF THE ARCH. 



All must admit that any attempt to fix the date of antiquities is a 

 dangerous task : that all who steer amidst the shadows of the past are 

 subjects of suspicion and mistrust, is also true. Yet though I do seek 

 the region of doubt, and, like the antiquary, revel for a little amidst 

 problems and enigmas, I trust the importance of the subject may 

 guarantee me in some measure from the fate predicted. In throw- 

 ing out a few hints then, upon the "origin of the arch," wrap|)ed as it 

 is in mystery, it is not from an idea that to fix the period of its birth 

 is vital to art, but rather that to assign to the relics and fragments of 

 antiquity their proper age, seems virtually to guide us into the spirit 

 of past times. Thus we shall be prevented from identifying much 

 that is curious and singular in design, or grand in invention, with a 

 barbaric sra ; when a more civilized race might more consistently 

 claim It. 



Rome, we say, deserves credit for this invention, because Livy, in 

 allusion to the "Cloaca maxima," remarks, that Tarquinius Priscus 

 drained the low grounds of the city about the Forum, and the valleys 

 lying between the Palatine and Capitoline Hills, by carrying sewers 

 from a higher level into the Tiber. (Lib. i, c. 38.) But the drain was 

 unfinished, and Tarquinius Superbus completed it, for he adds, " Tar- 

 quin the Proud made the great subterranean cloaca to carry olT the 

 filth of the city, &c. &c. (Lib. i, c. o(J.) 



Let us presume Livy to be correct, and that Tarquin really con- 

 structed that magnificent work ; still we cannot conceal the statement 

 of Herodotus and Strabo in their description of Assyrian monuments, 

 &c. We may admit, perhaps, the cloaca maxima as a work of the 

 Romans, but if Strabo be an authority, the arch was instrumental in 

 the construction of the hanging gardens of Babylon, which must have 

 been raised somewhere about izM years before Christ. Authorities 

 may and do disagree as to the real author of those works, but that the 

 pile of terraces w as sustained by vast arches, raised upon other arches, 

 seems indisputable. (Strabo, 1. xvi, p. 73S.) Then, again, as to the 

 date assigned to them, v\hether we take Ktesias or Herodotus, still 

 their date was very long before the building of Rome. Thus it fol- 



* We have frequently practised this method in copying railway plans and 

 sections in the c. untry — using common window class lor the purpose, and 

 found a great saving of time in cumparisoa with the uommon niethud of 

 pricking ilirough. 



