62 



THE CIVIL EiSGIXEER AND ARCHITECT'S JOURNAL. 



LFebhuary, 



feared tlie vessel would roll and loss to such an extent, as to prevent the 

 proper maiiaKement of the instruments, or keep the needles in their necessary 

 vertical position. It was, therefore, decided on to pay out 3,000 ft. of 

 insulated wire along the mouth of the harhour and the side of Ihe pier — 

 one end heinp connected with the telegraphic arrangements at the Folk- 

 stone station, thus being in direct comrnunicaiion with London, and the 

 other attached to an instrument on hoard the Clementine, at anchor in the 

 harbour. All the arrangements having heen completed hy half-past 

 12 o'clock, a message was sent to London, to apprise that all was in readi- 

 ness, after which a continuous correspondence was kept up between the 

 Clementine and the stations of London, Ashford, Tonliriilge, and Folkstone. 

 At four o'clock the submerged wire was drawn in and coiled up, and was 

 found not to have sustained the slightest injury. The experiments were, it 

 is stated, in every respect highly successful; the length of wire in the sea 

 forming apparently not the slightest impediment to the perfect and free 

 transit of the galvanic current. 



The wire employed was not made expressly for the occasion, hut had heen 

 constructed for the Merstham Tunnel, where it was found that not only 

 the damp on the wires affected the galvanic current, hut was still further 

 interrupted hy the steam from the engines, impregnated with acid and 

 earthy matters. Its size is No. 16 copper wire, covered to a thickness of 

 about J inch diameter with gutta-percha, under a patent hy Mr. Foster, of 

 the gutta-percha manufactory, Streatham, and similar wires will in future 

 he employed in all the tunnels on the lines, which places have heen found to 

 cause the only obstructions which present themselves to the free working of 

 the system. 



The telegraphic instrument employed was one constructed hy Mr. 

 Walker, on a plrin to avoid any action from atmospheric electricity. The 

 galvanic coils are mounted on wheels, and the needle is brought to a perpen- 

 dicular with the greatest facility hy turning a stud, which causes the coil 

 to pass in a direction opposite to tliat to which the needles had heen de- 

 flected. The conductor for the atmospheric electricity consists of a vertical 

 wire, furnished with radiating points, and a bobbin of wire of a much finer 

 teiture than any other in the instrimient. This is surrounded by a small 

 brass cylinder, connected with the earth, and any overcharge of electricity 

 hums the fine wire and escapes. This occurred in one instance at Tun- 

 bridge Wells, during a thunderstorm, a short time since. 



FORCE OF SCREW-DRIVERS. 



Sir — Will you oblige me by answering the following questions in your 

 next number.' We will suppose, for instance, a screw of a certain size is to 

 be driven ; with a short driver you are obliged to use great force to accom- 

 plish it — but with a long screw-driver there is less force required. You 

 will perhaps, therefore, explain why millwrights and engineers use a short 

 shaft, or endeavour to get the power to act upon the resistance as close as 

 possible. It appears that these cases are exactly opposite. I hope this is 

 sutBcieutly plain for you to uuderstanJ what 1 want. 



A CoN'ST.'iNT Reader. 

 London, Jan. 6th, 1849. 



[The force required to turn a screw does not depend on the length of the 

 screw. driver. In supposing that a screw may be driven more easily by a 

 lone screw-driver than hy a short one, the very common error is involved hy 

 which a setisalion of exertion is mistaken for force. Let the actual force 

 required to drive screws of the same size and kind into a certain piece of 

 uniformly compact wood be measured — not roughly, hy the fatigue of the 

 arm — hut accurately in pounds and ounces — by means of a dynamometer, 

 and it will be found that, allowing for slight irregularities which are una- 

 voidable in such experiments, the force required is the same whether the 

 screw. driver be six inches or eighteen inches in length. The reason why the 

 longer driver requires less exeition in turning large screws is, that it can he 

 more firmly grasped, and allovps the workman to bring his muscles more 

 easily into play than is practicable with the shorter instrument. The inves- 

 tigation of the power required in turning screws resembles the mechanical 

 principles of the wheel and axle, where a weight suspended from a rope 

 coiled round the wheel in one direction resists the rotative power of a 

 weight attached to a rope coiled round the axle in the opposite direction. 

 When the wheel is just on the point of turning, the weight applied to it is 

 to the other weight as the radius of the axle to that of the wheel. In the 

 same way, when the screw is just on the point of turning, the tangential 

 force resisting its rotation is to the external turning force applied tangen- 

 tially to a round handle as the radius of the handle to the radius of the 

 screw. 



The reason why engineers make driving-shafts as short as possible, is be- 

 cause short shafts are cwCecM^jan'iws less likely to be twisted by torsional 

 strains than long shafts. — Editor.] 



NOTES OF THE ItdONTE. 



Ammonia Destructive to Leather. — Ammnniacal emanations from manure 

 in stables are most pernicious to leather, it being rendered quite brittle and 

 useless in a very short period ; consequently, harness ought never he allowed 

 to hang up in stables. 



The appearance of Old Oak may he obtained hy exposing any article of 

 new oak to the vapours of aininonia. Every variety of tint may be olitained 

 according to the duration and temperature of the volatile compounds. A 

 nf w oak carved arm-chair exposed to the vapours of amnionia, will in about 

 twelve hours have all the appearance of its being made 200 years since; and 

 any other wood similarly exposed, will obtain the appearance of oak. 



Cast Iron Pipen Enamelled v,n»\A be a valuable acquisition in obtaining 

 pure water. A corresponrlent inquires whether pijies have heen so prepared : 

 an answer from any of our readers will he acceptable. 



Earlhenvare Pipim/. — .\lr. Murray, in the Mining Journal, in answer to 

 a correspondent, considers an internal glaze for the earthenware pipes 

 altogether unnecessary. Earthenware pipes for the conveyance of water 

 should be so deeply laid in tlie earth as to he unaffected hy the agency of 

 frost, lest the water absorbed by the porous earthenware in the act of ex- 

 pansion by freezing should rend the pipe. The application of gas tar to 

 the pipes, when imbedded, as an external coating, would act as an insulator 

 in reference to external temperature, and operate as a defence against the 

 influence of frost. 



Zinc Paint, — Some experiments were recently made at the Veille 

 iMoulagne Zinc Company's Olfices, on zinc and white-leaf! paint, by sub- 

 mitting them to a stream of sulphuretled-h)drogen gas, wheo the white- 

 zinc paint remained unchanged anil the white lead paint was turned quite 

 hlrick. Some specimens of external painting were also shown of both zinc 

 and lead, which had been painted fiir some months; the zinc paint still 

 reiained its whiteness, whilst (bat of the lead had very much changed. 



Wrought Iron Cofferdam. — Last month the experiments undertaken by 

 Mr. Brunei, at the instance of the Admiralty, for carrying the railway bridge 

 across at Saltash, for the Cornwall Railway, were tirought to a sticcess- 

 ful close. For the purpose two old gun-brigs, purchased of the eovernraent, 

 were moored over the spot, and a wrought-iron cylinder, ot | inch boiler 

 plates, strongly rivetted together, 85 feet high, and 6 feet diameter, and of 

 28 tons weight, was sunk in pro/undis. The necessary apparatus for pump- 

 ing out the water was then applied, and the experimenters, who alterwards 

 descended to the bottom of the cylinder, had the satisfaction of finding that 

 at 11 or 12 feet below the mud, there was a foundation of solid rock for the 

 piers. The bridge will be of large dimensions, the Admiralty requiring that 

 it shall have a clear width of 300 feet between the [licrs, and a clear height 

 of 180 feet above high-water mark. Over it will pass the entire passenger 

 traffic from Plymouth to the Land's End. 



Dover Harbour of Refuge. — We have again, says the Dorer Chronicle, 

 much pleasure in recording tlie successful prosecution of this gieat maiitinie 

 undertaking of the present age. On visiting the woiks the other day we 

 were quite astonished at the remarkable extent of progress made since we 

 last noticed them. The works are certainly conducti-d with an extraordi- 

 nary spirit of industry. This is evidenced by the fact that the timber 

 framework of this great sea harrier has been carried out upwards of 2t)() 

 feet from the point of shore at the Old Cheeseman's Head; and hy the aiii of 

 several diving-hells, helmets, &c., and a most tiiaslerly arrangement of 

 travelling cranes, the ponderous stonewoik has been securely bedded in 

 the chalk rock to a similar distance, and brought up almost to the level nf 

 high-water, within eight months. This compact body of beautiful masonry 

 contains, we believe, no less than 150,000 cubic feet of stone of large di- 

 mensions, and of the finest quality that this country can produi-e, and ^ives 

 good evidence of the ultimate stability of a structure, the beneficial effects 

 of which are already very apparent, inasmuch as the frequent heavy sea 

 caused by the prevailing south-west winds is materially checked at the har- 

 bour mouth, and the entrance of vessels into this desirable haven during a 

 gale is now rendered almost a matter of ease and certainty. In addition to 

 the extraordinary appliances already referred to, there is a fine steam-engine 

 at work, driving several sets of mortar and cement mills, and a remarkable 

 crane for unloading vessels. This engine is worked with all the docility of 

 a child, and has within these few months discharged about 15.000 tons of 

 stone, and all too with the most careful and steady results. Altogether, the 

 works present the ajipearance of a more successful contending against the 

 destructive action of the sea at this much exposed portion of the coast, 

 than has ever been before attempted here. The operations have been 

 inspected by engineers, royal, civil, and practical, all of whom have 

 expressed their entire confidence in the speedy and satisfactory com. 

 pletion of a work so gigantic and so eminently calculated to save hun- 

 dieds of lives, and thousands of pounds' worth of property. Several very 

 high gales, with tremendous seas from the Atlantic, have lately waged their 

 fury upon it, but no damage has been sustained further than occasional in- 

 terruption to the working of the machinery upon which so many of the 

 operations depend. The successful results here shown are no doubt to he at- 

 tributed to the high standing of the engineers, and the spirited en- 

 terprise of Messrs. Lee, the contractors, who always avail themselves of the 

 most valued expedients that science and practice can provide, and which are 

 so hig'ily calculated to bring this great monument of human skill and ol a 

 nation's resources to a satisfaclorv condusiou. 



