and Dale Street; or, as in Fig. 205, with two distances from the angles of Church Lane and High Street and from the end of the "Crown Inn" on one side, and from a point measured along the face of the hotel from George Yard; or, in Fig. 206, from the two angles of the Market Place and those of Market Street. It is recommended by some writers to take "lamp-posts, corners of buildings, &c.," as " objects at a distance," forgetting that inasmuch as instrumental observation will be necessary at all points of divergence, such points will be of very slight service, inde pendent of their somewhat questionable applicability. Town surveying requires great care and patience, with a very considerable amount of method. It resolves itself into three distinct operations after the lines and stations have been determined: 1, the observation of the angles; 2, the chainage of the lines between these points; and 3, the detail measurement of the yards, gardens, buildings, &c. Taking Angles. There are two ways of taking the angles. TAKING ANGLES OF STREETS. 163 First by taking (with theodolite or prismatic compass) the angle which a street or road makes with the magnetic meridian, but which cannot be recommended in towns (although in villages it may be more practicable), in consequence of the numerous sources of attraction to the needle, such as tram-rails, lamp-posts, hydrants, man-holes, iron railways, &c. By the second and most reliable method the included angles of one or more lines are taken with the theodolite as illustrated in Fig. 207, where a line along Station Road terminates at the junction of three streets. Here the theodolite should be planted, and after being carefully adjusted, the angle between Station Road and High Street (90° 30′), between High Street and West Gate (71° 00'), and between West Gate and Mill Street (46° 00'), should be observed; the sum of which WEST GATE RANGING ROD Cross Hairs of Telescope Fig. 207. Fig. 208. should be 207° 30′. Now take the angle between Station Road and Mill Street, which should be 152° 30', or the difference between 360° 00′ and 207° 30′. Objection to Lamp-posts, &c. - My reason for not taking lampposts, corners of houses, &c., as distant points upon which to fix the telescope, is that in the first place they can only be of a temporary character, and a lamp-post especially is not sufficiently defined for the purpose even if it be perfectly perpendicular. If spikes are driven in the streets or roads at points of intersection, it is surely the most accurate method for a chain-man to hold the point of the rod upon the spike, which point is only to be taken, for I cannot impress upon the student too strongly the necessity of observing the bottom of the rod as in Fig. 208 in all surveying 93-38 HOLLAND A ROAD Fig. 209. operations, whether it be simple chainsurveying or with a theodolite. By this means we have an absolute point upon which our instrument will in turn be placed, so that with necessary care all our observations should be accurate, and judgment (often very misleading) as to which is the actual centre of a far distant lamp-post is obviated. In consequence of the circuitous nature of many streets in European towns-which, unlike American cities, were evidently never laid out with any idea that it would be necessary to survey them it is often impossible to get a straight line from end to end. Take the case of Fig. 209. Here we have, at a, to take the two angles right and left equal to 180°. At B we should take the angle between A and Bemer Street, and that between Bemer Street and c, whilst to test our work we must observe the angle CBA, all three being equal to 360°; at c, the included angle BCD and its supplement at D, all four angles which should equal 360 deg. Now a very natural question might be asked: "Yes, I see how you do such a street, and if I have taken the angles and distances between the points correctly, all well and good: but how do I know that it will all fit on to the other parts of the survey?" I will endeavour to clear this question up. In Fig. 210 we have a sketch map of part of the town of Leatherhead, of which it was desired to make a detailed survey. It was found impossible to run a larger base - line through the principal streets than the line A B, about 1,200 ft.; but CD, 2,050 ft. could be tied on to the other portion of the survey outside the 1 town, and as it is always best to take the longest line for a base we adopted CD. It so happened that A B is so situated that it was possible to set out the line at right angles to cd, which of course was of immense advantage. But with the exception of the short line gh, this is the only case in which it was possible. Taking the upper portion first, it will be seen that Gcat the ends of C D and of ag with A B circumscribed this portion of the town; on the line a B, stations at a, a', b', c', e', and n were left, whilst on ac, stations b, c, and d; and on the upper part of CD, h and l. Strictly speaking, the angles aGcand GCDshould be taken as well as Gas and cna; although it is argued that if these latter two angles are accurately taken, and the distances Ga, an, and nc are carefully measured, then by calculation in the one case and measurement in the other the length ac will be proved. I say it is so argued, but my own opinion is that whilst about it the most satisfactory way will be to take the angles with the theodolite, especially as we must take the angles GbE, GCf, Gdg. It is not absolutely necessary to take the angle bef, but those cfj, f ja, gjk, and klc are imperative; as are also a a' E and a c'm, the angle a a' E is not necessary, but the line a' E should be carefully measured as a tie; gh need only to be measured from their respective points and will act as a check on dg and ch. Similarly, if the angles a b'F and And be carefully observed in the lower portion, it is not absolutely necessary to take more than btn and usq, as all the other lines tend to check the trapesium b'FDn; for tn and væ in one direction and ry' and xz in the other are as complete checks as can be wanted. Thus will be seen the relative systems to be adopted in street surveying, but let it never be forgotten that there should be no question about the angle any street may form with another. The line CD was able to be produced until it fitted into the system of triangulation for the survey of the district around the town. The traffic in the streets is a considerable drawback to the operations of the surveyor, whilst from twelve till two and after four o'clock are periods towards which he looks with dread, as at these times he is sure to be accompanied or surrounded by a powerful contingent of the rising generation, whose inquisitiveness and love of mischief are of the greatest impediment to his progress, and test his patience and temper to the utmost. As to the Chain. -For ordinary small scale plans the measurements may be taken with a 66-ft. chain, but when great detail and accuracy are requisite the 100-ft. chain is the best. The offsets should be taken in feet and inches with a tape; those at right angles to the chain-line require the greatest care and are best set out with an ordinary square (as it is seldom, from the narrowness |