1843. J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



249 



The compound sillomftre consists of the same mechanism, Fig. 2, 

 with this addition, that the power which moves the index M, is ap- 

 plied at the same time to a watch N, and accelerates its movements 

 in proportion to the intensity of the moving power, or as the vessel 

 quickens her speed. A second watch R, is placed by the side of the 

 first, in order to show how much the former gains upon the latter; and 

 knowing that for every six seconds of gain the vessel will have made 

 a mile, it is easy to know the distance run. It is evident that this 

 compound instrument is very superior to the simple one, but its accu- 

 racy depends upon the regular going of two good watches, a result 

 not very easily obtained at sea. 



The Sub-Marine Thermometer is a very delicate instrument com- 

 posed of a ribband formed of two metals of unequal contraction and 

 expansiou, as platina and silver, and rolled in the form of a helix A, 

 Fig. 3, round an axis B, which turns as the temperature of the water 

 varies. This motion by a train of wheels and pinions is immediately 

 communicated to two pointers on a graduated dial on deck, and which 

 may be read off easily to hundredths of a degree. 



The whole of this apparatus is enclosed in a metal tube, which 

 passes through the bottom well aft in the run of the ship. The helix 

 or thermometer is therefore always at a certain depth in the water, 

 say 10 feet below the surface; and it shows instantly every change in 

 its temperature. 



As few observations have been regularly made on the temperature 

 of the water of the sea at a certain depth, this machine may lead to 

 some novel results. 



The Sleam Indicator points out the temperature and consequent 

 pressure of the steam in the boilers ; it is composed of a ribband or 

 blade of two sensitive metals of unequal expansion, turned in a spiral 

 form; one end is fixed to the tube or pipe in which it is contained, 

 the other connected with a spindle bearing the pointers which indi- 

 cate the temperature of the steam on a dial on deck, in degrees and 

 tenths of a degree. This instrument is connected by a small pipe 

 with the boiler or steam chest through which the steam reaches the 

 spiral, which instantly causes any variation in temperature to be 

 shown by the dial on deck : in high pressure engines this may be 

 found useful. 



The Derivometre is an instrument somewhat on the principle of the 

 sillometre, and intended to measure the drift of a ship ; this is done 

 by a vane placed on the keel, connected by a rod with a dial — the 

 vane of course takes the opposite position to the drift of the vessel, 

 which is communicated by the turning of the rod to the pointers on 

 the dial on deck. 



The Interval and External Thermometer, as its name indicates is a 

 highly sensitive thermometer, so placed against the wall of an obser- 

 vatory or house, as to show the temperature of the air within and 

 without. The two pointers which mark this are on the face of the 

 same dial. 



The report and log show that the sillometre indicated every varia- 

 tion in the speed of the vessel, even the alteration caused by a single 

 spoke of the helm was perceptible, and putting the helm hard over 

 caused the ship to lose half her way almost immediately ; as the dial 

 of the instrument is placed on deck, and the index or pointer very 

 conspicuous, the officer of the watch without any trouble may observe 

 it at every turn he takes on the quarter deck ; and it is obvious that 

 none but the most inattentive person can fail to have a much more 

 correct knowledge of the rate of the vessel's going than he can from 

 heaving the common log once or twice an hour. The sillometre will 

 also enable an officer easily to ascertain the best trim of a vessel ; the 

 difference caused by shaking out a reef or by making or shortening 

 sail ; and in a fleet would enable a ship to keep her station by night 

 or by day with great steadiness ; and lastly it impresses very strongly 

 on the observer the absolute necessity of good steering and giving 

 very little helm when in chase or on a trial of sailing, or at any other 

 time when speed is of importance. 



The Steam Thermometer has also a dial placed on deck so that the 

 officer of the watch can tell at any moment whether there is a suffi- 

 ciency of steam or the contrary, and can thus check the wasteful ex- 

 penditure of coal; it would point out too the possible, but highly im- 

 probable occurrence of no water in the boilers, or an undue increase 

 of the temperature of steam from any other cause. Its chief value 

 however would be shown in a high pressure steam engine when it 

 would give immediate warning of any approach to such a degree of 

 temperature or pressure as might be dangerous. 



The Sub-marine Thermometer remains constantly at a depth of about 

 ten feet below the surface of the water, and owing to its being formed 

 of platina and silver is extremely sensitive, and thus every change in 

 the temperature of the sea will be shown at once on the dial on deck. 

 As in the Atlantic Ocean and other deep seas, the deep water is 

 said to be warmer than the shallow ; it probably would there show, by 



mere inspection, the approach to shoals, rocks, or land, and serve as 

 an excellent warning. At this season of the year however in the 

 shallow waters of the North Sea we observed no such effect, on the 

 contrary the temperature of the water gradually decreased from 50'' 

 Fahrenheit at Woolwich to 44£ at about 20 miles to the eastward of 

 the North Foreland, and as gradually increased on our returu to the 

 same point. 



Possibly as the summer advances this may be different, and in order 

 to discover when the change of temperature takes place, I have di- 

 rected the instrument to be registered every two hours night and day. 

 As the thermometer is highly sensitive and may be read off witli ease 

 to hundredths of a degree, and agrees perfectly with the best mercu- 

 rial thermometers, it may possibly furnish some novel results of value 

 to the philosopher as well as to the navigator, since I am not aware of 

 the existence of any continued series of observations on the tempe- 

 rature of the sea at all seasons of the ye ir. 



WESTMINSTER BRIDGE. 



Report to the Speaker, by Messrs. Walker and Burges, on the altera- 

 tions proposed by Mr. Barry. 



Sir, — As that portion of Mr. Barry's report to His Royal Highness 

 Prince Albeit (on the decorations, additions, and local improvements 

 connected with the new Houses of Parliament) which refers to West- 

 minster-bridge, may naturally lead to the opinion that our plans, made 

 under the direction of the Bridge Commissioners, were confined to the 

 repairing and extending of the foundations, for our superintendence 

 of which he kindly compliments us ; we consider it, therefore, a duty 

 to prevent such a mistake, by stating, that the designs, estimates, and 

 the contract with Mr.Cubitt, included the repair of every part of the 

 bridge, the " removal of the present steep and dangerous acclivities, 

 and the lowering of the parapet and road-way to the lowest possible 

 level" that appeared at the time to be consistent with the safety of the 

 present arches. The second contract with Mr. Cubitt, is for lengthen- 

 ing the piers, which are being carried to above high water level, to 

 receive arches for widening the bridge twelve feet. It will then be of 

 the same width as London-bridge. All, in fact, that we have done 

 to Blackfriars-bridge, is designed and contracted for, 1 to be done to 

 this bridge, with the very important addition of the preparation for 

 widening. The steepest part of Westminster-bridge road-way will, 

 when the designs are executed, be as easy as that of Blackfriars- 

 bridge. That which rises one in fourteen, will be reduced to one in 

 twenty-four, and even this rise will be for only a limited length. 



To secure the foundations, which were in danger of beiug under- 

 mined by the scour consequent on the removal of old London bridge, 

 has been the first object. The supposed difficulty of doing so effect- 

 ually, was increased by the opinion entertained by Labelye, the origi- 

 nal engineer, and others since his time, that owing to quicksands, 

 coffre-dams could not be applied ; and the commissioners have been 

 desirous of removing all doubt on this point, before proceeding with 

 the spandrils, road-way, or parapet. Five out of the seven coffre- 

 dams have been built ; so far, we have been completely successful : 

 and while the water was excluded, all the work which was required in 

 repairing and lengthening the piers to above high water, has beeu 

 done ; seven out of the thirteen arches have also been repaired, as 

 the coffre-dams gave facility for the scaffolding necessary for doing 

 this. Thus far, therefore, our desigu proposed to, and approved by, 

 the Commissioners, corresponds with, and has anticipated Mr. Barry's; 

 but the idea of taking down the present semi-circular, for the purpose 

 of substituting pointed arches upon the same foundations, is not ours, 

 and we beg to state shortly, why we do not concur in the expediency 

 of this proposal. 



Mr. Barry's first argument for this change is, " that the pointed arch 

 will enable the road to be lowered, by materially reducing the thick- 

 ness of the crown of the arches, within what is considered necessary 

 for arches of a circular form." Now, we consider that the whole 

 thickness of the stone-work and covering of the present centre arch 

 may be reduced to about seven feet, which is the same thickness as 

 Mr. Barry's ribs, arch and covering, measured upon his section ; so 

 that, even supposing the principle lie states, of the pointed arch re- 

 quiring less thickness than the circular arch, to be correct, he obtains 

 no reduclion in thickness, and only lowers the road-way, by lowering 

 the soffit of the arch. The generally approved theory of arches is 



1 The commissioners have power to suspend or supersede the contract in 

 respect of any works not commenced. 



