* 



riKus 



PIEZOMETER. 



under a head 'f U-r of not lea* than 37 feet, proves that it would b 

 po**ible to nuke a much greater ue of that material thau is usually 

 cone in England ; but of whatsoever material the pier* may be formed, 

 the nootwuty for protecting the foundation* frum the undermining 

 action* of the current*, or of the ground swell, must remain the same. 



her practical remark* to be made with respect to the execution 

 of niMonry pier* are, that the; roust settle equably throughout their 

 v. linle ma** ; that no opening* should be left by means of which water I 

 could get into the Interior, either directly, or by syphonment ; that ( 

 the masonry should be protected against the abrasion of the aUu- . 

 vions carried forward by the currents, and that the ships lying 

 alongside the piers should not bear directly against the face of the 

 masonry, for which purpose fender pile* are used ; finally, all abnipt 

 projection* must be avoided whether in the plan or the elevation of 

 the piers, and the surface of the roadway must be carefully laid, so as 

 to throw off all the water which may break over the piers. It is usual 

 to make the width of the roadway*, in the body of the work, from 10 

 to 28 feet, and to increase that width, at the heads, to from 80 to 50 

 feet ; the body of the pier being kept about 10 feet above the level of 

 high spring tides, and the heads about 12 feet above the same level. 

 Generally speaking, a lighthouse is erected near the extremity of ft 

 pier; fog bell* and signal guns are fixed ; and the necessary bollards, 

 or mooring posts, reeving pullies, capstans, and landing staircase* are 

 to be provided. It is curious that the softer calcareous stones are 

 nearly as much affected by the boring molluscs as wood is affected by 

 the limnoria and teredo ; and that the solenidse, pholidtc, and litho- 

 doini, exercise fearful ravages upon that class of stones in some 

 place*. Where those animals abound, or where the littoral current* 

 carry forward much alluvial matters, it becomes necessary to employ 

 the more resisting siliceous rocks, or the granites. 

 3. The questions connected with the interferences likely to be 

 produced by the erection of a pier upon the outline of a coast are 

 often of extreme importance, not only to the harbour it is desired to 

 create, but also to the whole of the surrounding district ; and they 

 must, therefore, be very carefully and attentively studied before such 

 works are commenced. Unless there should exist some local cause of 

 disturbance, it will, in fact, be found that the alluvial matters detached 

 from cliffs and sea-shores by the action of the sea, will be carried 

 forward by the flood-tide until they meet with some impediment able 

 to check their advance ; they then begin to accumulate behind this 

 shelter until the angle is filled in, when the onward progress of the 

 alluvions is resumed. If the littoral current should sweep across the 

 mouth of the pass between the piers, it may carry the sand and shingle 

 past the latter ; but under almost all circumstances a large portion of the 

 finer matters in suspension will be carried into and serve to silt up 

 the harbour. The some thing will occur with a few trifling modifi- 

 cations when single solid piers are carried out from a shore, whether 

 their plan be straight or curved, or whether they be constructed in 

 the sea or in rivers; the alluvial matters will accumulate on the 

 upside to the current, and it often happens (as it did lately at Dover) 

 that, until the advance of the shingle again brings some light moveable 

 materials to protect the fore shore, the newly-created counter-current 

 will wear away the original outline of the coast on the downside of 

 the pier. 



The Roman engineers appear at an early period in the history of 

 engineering, to have recognised the importance of these laws, and they 

 constructed their ports habitually upon a series of open arcades, with 

 the avowed intention of interfering as little as possible with the 

 advance of the littoral currents. In modern times the use of wooden 

 or of iron open jetties has been recommended for the same purpose ; 

 but all these methods of palliating the evils of the interference with 

 the progress of the alluvions are open to the serious objection that 

 they leave the interior of the harbour without protection from the 

 undulations of the open sea ; and it therefore follows that if the com- 

 merce of the harbour should be important, the piers should be rendered 

 sufficiently solid to intercept the normal deposition of the alluvions, 

 even on the condition of constructing defence works for the shore* on 

 the down side. Any materials which, under these circumstance*, may 

 be carried round the heads of the piers must be removed, either by 

 mean* of dredger* or by periodical sluicing. [SLUICE.] The practice 

 of the most scientific engineers of the present day, it may be added, 

 tend* toward* the uae of dredgers in preference to sluicing; both on 

 the score of economy and of efficiency. When the alluvial matters are 



cd by sluicing they are in fact only carried to the distance 

 winch the transporting power of the water can command; and then 



>lmoftt always are thrown down in the form of a bar, across the 



of the harbour. It would really appear that, under these cir- 

 cuintances, it i* wiser to provide for the extraction of the alluvions 



liiiiery, proportionate to the quantity brought in within certain 

 cKiuiite period* ; especially as it would then be easy to construct the 

 PUT* in plan, solely with reference to the physical conditions of the 



y as affecting the navigation, instead of (a* in the cose ol 

 resorting to sluicing) building the piers for the purpose of guiding 

 the outpouring waters. 



LambUrdie i* the engineer who ha* studied the question of the 

 advance of alluvial matter* on a sea-shore with the most skill, attention, 

 and ftiiocen ; and it is to his works, or to those of Zendrini, or of Sir 

 1 1 I > labeche, that the student of this nubjcct must be referred. The 



leading principle* of this branch of the science of hydraulic engineering, 

 o far a* they are likely to affect the construction of pier* or harbours, 

 may, however, here be stated briefly a* follows allowance of course 

 being made for local cause* of disturbance. 



At the base of steep cliffs the alluvions follow the outline* of the 

 coast, and they have, under ordinary circumstances, but little tendency 

 to change their positions ; in deep bays they will assume a curvilinear 

 outline, whose concavity will be turned towards the sea in the din 

 of the prevailing wind, unless where modified by the line of tin' 

 current. If the directions of the prevailing wind and of the current 

 should be parallel to the shore, the transporting power of the current 

 to carry forward alluvial matters will be less than when the dii . 

 of those forces assumes an angle of 45* to the coast; and wh< 

 wind blows perpendicularly to the shore, the waves may exercise a 

 great effect in abrading the latter, but the movement of the alluvions 

 will be almost imperceptible. A bay, or a harbour, whose axis may be 

 in the line of the prevailing wind will, therefore, bo exposed to become 

 rapidly silted up; and this result will take place with increased 

 rapidity if any land waters bringing down matters in suspension 

 the uplands should discharge themselves into the bay. One important 

 remark to be mode with respect to the deposition of alluvial matters 

 n the embouchures of rivers receiving the flood-tide, under circum- 

 stance* which should allow the latter to carry forward the shingle it 

 previously detached, is, that the alluvions so carried in are of far more 

 serious importance in their effect* upon the accumulations n: 

 piers or harbours constructed in those rivers than ore the alluvial 

 matters brought down from the uplands. There is, in fact, every 

 reason for believing that in such rivers as the Thames, the Seine, or 

 the Rhine, more alluvial matter is carried in from the sea than the 

 land floods can transport to their respective mouths ; which, it may ba 

 added, is another reason for constructing open piers in such situations, 

 because they offer lea* resistance to the natural laws of such localities. 

 After all, engineering is essentially the science of adapting the mean* 

 to the end desired; and economical conditions of first outlay may 

 often render it expedient to depart from the strict application of even 

 strictly demonstrated laws ; but the attempt to run counter to those laws 

 will always be productive of disastrous results ; and in no cose is this 

 more true than with regard to the effect of piers upon the outline of a 

 coast. The histories of Ramsgste, Dover, Calais, or Dunkirk harbours, 

 or of the ports, so called, of refuge on our eastern coast may be 

 referred to as illustrations of this remark. 



The Brighton chain-pier may be referred to as an illustration of an 

 ingenious method of constructing works of this description without 

 producing any interference with the movement of the alluvions ; but 

 piers with such wide intervals between the points of support give no 

 protection from the agitation of the waves. 



PIETISTS, the name given in the 17th century to a kind of 

 German Methodists or Evangelicals, who, being members of the 

 Lutheran Church, were dissatisfied with the cold dogmatism of the 

 generality of its clergy, and felt the want of a revival of religious 

 feeling and of practical piety and charity. Without separating tin m- 

 selves from the church, they instituted meetings called " Collegia 

 Pietatis," from which the denomination of Pietists was derived. 

 Philip Jacob Spener, a divine of the Lutheran Church, who was 

 preacher at Frankfort and afterwards at Dresden and Berlin, was the 

 chief promoter of these meetings, which began about 1670. [Si 

 in Bioo. Div.] 



PIEZOMETER (ntfu and iterptu). Under ELASTICITY are noticed 

 the various attempts to measure the compressibility of water and other 

 fluids, and reference is made to Professor Oersted's instrument by 

 which the problem wossatisfactorily solved. It consists of a strong glass 

 cylindrical vessel A B c D with a smaller cylinder A B E F scrowed into the 

 top, containing an air-tight piston K worked l>y a screw ; II is u glass 

 bottle, into the neck of which is ground a capillary tube a a, open at both 

 ends, of fine bore, and each inch of its length must express a precise 

 fraction of the contents of the bottle. This is done by weighing how 

 much mercury the bottle will hold, and how much an inch of the 

 bore of the tube. In some of Oersted's tubes each inch in length 

 was found to hold ra$mths of the contents of the bottle. Let us now 

 suppose the whole of the apparatus to be filled with water : any pres- 

 sure upon it which causes its surface in the tube a a to descend one 

 inch, will have compressed it by tK^knths ' '* s bulk. The scale 

 attached to the tube was graduated, each inch into 10 parts, so that a 

 depression of the water in the tube through one of these division* 

 would indicate a compression of two-millionth*. The apparatus being 

 arranged as in the figure, only with the piston K at the bottom of tho 

 short cylinder in contact with the water which fills tho large cylinder 

 and the bottle si, the piston is screwed back towards EF, and as it 

 recede* water i* drawn into the vessel by the. siphon B p from the 

 vessel r. A cock is then closed in the siphon, and on screwing tho 

 piston downwards tho pressure is propagated through the w.r 

 the cylinder, and also through the tube a a to the water in the bottle, 

 Mieh pressure being of course precisely the same within and without 

 the bottle. A separation is made between the water in the tube a a 

 and that in the large cylinder, by means of a bead of air contained in 

 the glass cap r, which yielding to the pressure descends the tube a a, 

 and serves as an index finger to the scale. The amount of pressure 

 1 by driving down the piston is measured by means of the tube 



