590 



UEl'UKl — 1S84. 





Notwithstanding the short duration of the sound of explosive signals, 

 they arc rendering valuable service to the mariner in cases where the 

 siren, or any other powerful form of sound signal, could not be applied, 

 for want of space. The rapidity of combustion, and consequent loud 

 report of charges of gun-cotton, compared with equal charges of gun- 

 powder, together with the safety in storage of the former, have led the 

 Trinit}' House to adopt gun-cotton largely for coast fog signals ; and at 

 the suggestion of the late Admiral .Sir liicliard Collinson, K.C.B., Deputy 

 Master of the Trinity House, rockets are emi)lo3cd for carrying one or 

 more charges of gun-cottoii up to a height of HUO to 1,U00 feet, and then 

 causing them to explode. These rockets are most usefully employed at 

 stations wliere obstacles to the sound-waves occur in the seaward arc over 

 wliich they are required to be sent. Tiio sound thus elevated has been 

 found to surmount such diiliculties most successfully. Gun-cotton has 

 also been found to provide a very efficient coast fog signal at isolated 

 stations on rocks or shoals where previously, from want of space, nothiug 

 better than a bell could be applied. On Plate IV. is shown, for this 

 form of signal, the appai'atus which J have lately designed, and which is 

 now adopted by the Trinity House. To the roof of the lighthouse lantern 

 is attached a light wrought-iron crane, the jib of which is promptly raised 

 and lowered by a worm-wheel and pinion, worked by a hand-wheel inside 

 the lantern. AVhen the jib is depressed tlie lower end reaches near the 

 gallery outside the lantern, where the light-keeper suspends the charge 

 or charges of gun-cotton with their detonators already attached to the 

 electric cable or cables, which are carried from tlie end of the jib to a 

 small dynamo-electric firing machine placed inside the lantern. After 

 suspending tlu' charge or charges, the light-keeper returns to the lantern, 

 when he raises the jib to the upper position, where the charge or charges 

 are fired nearly vertically over the glazing of the lantern, and thus with- 

 out causing any fracture of the glass. 



Tlif Kcic Eddijiitonc Lijhiliouso. 



In a paper contributed to the British Association at the Plymouth 

 meeting in 1877 on the Eddystone Lighthouse, I explained the necessity 

 for erectii g a successor to the justly celebrated model of Smeaton, in con- 

 sequence of the portion of the gneiss roi'k on which it was founded having 

 been seriously undermined and shaken, also owing to the light being 

 frequently eclipsed by each heavy wave dui-ing stormy weather, thus im- 

 pairing and .altering its distinctive character. I nov/ propose to supple- 

 ment my remarks on ' Impi'overaents in Coast Signals ' by a brief 

 I'cfei'ence to the new lighthouse. To the diagrams of the new structure 

 shown I have added diagrams to the same seide of Smeaton's lighthouse, 

 and the two that preceded it, viz., that of Winstanley, erected in lO'JC), 

 and destroyed by a storm in 1703; the other of Rudyerd, commenced in 

 1706, lighted in 1708, and destroyed by fire in 175-"). 



The new tower at the Eddystone is a concave elliptic frustrum standing 

 on a cylindrical base 44 feet in diameter by 2'2 leet high ; the generating 

 curve of the frustrum has a semi-transverse axis of 173 feet, and a semi- 

 conjugate axis of 37 feet. The mean focal plane of the light is 133 feet 

 above high water, having a nautical range of 17^ miles. The tower 

 consists of 2,171 stones, containing 02, 133 cubic feet, or 4,GG8 tons of 

 granite. All the stones aie dovetailed together both horizontally and 



