738 EEPORT— 1889. 



to unlock the points, the points themselves then pulled over and relocked ; the 

 second notch would perform a similar series of operations at the other pair of points 

 in the cross-over road ; the third notch would lower the home and the fourth the 

 distant signal. In the present system of signal apparatus, six levers would be re- 

 quired to work this operation, and eight distinct movements would have to be 

 made : unlocking each pair of points, moving them, relocking them and then 

 working the two signals. The same lever, if moved to the left, would perform a 

 similar series of operations for a train passing in the opposite direction. The valve 

 rods are so interlocked that if from any accidental cause the points are not pulled 

 fuUy over, the signals cannot be lowered. 



SATURDAY, SEPTEMBER 14. 

 The following Reports and Papers were read : — 



1. Report on the Investigation of the Action of Waves and Currents on the 



Beds and Foreshores of Estuaries iy means of Working Models.-^See 

 Reports, p. 327. 



2. Report on the Bevelopment of Graphic Methods in Mechanical Science. — 



See Reports, p. 322. 



3. Ships for the Carriage of Petroleum. By A. R. Liddeli. 



The petroleum ship industry began on the Tyne about five years ago, when the 

 steamship ' Gliickauf ' was built by Sir W. G. Armstrong, Mitchell & Co. for Herr 

 Eiedemann of Bremerhaven. Some early ships — ^the ' Vaderland,' ' Nederland,' 

 and ' Switzerland ' — were built by Messrs. Palmer & Co., of Jarrow, in 1872 to carry 

 petroleum in bulk, but they were never employed iu the trade. Prior to 1886 

 some ordinary cargo vessels underwent costly alterations, and were converted into 

 petroleum carriers, but were only partially successful. American petroleum has a 

 specific gravity of "8. It varies with the temperature to the amount, of about 

 2 per cent, for a difference of 40° F., and it gives off a vapour which is very 

 inflammable. Petroleum was at first carried in wooden sailing-ships, in barrels or 

 boxes in the hold ; but under these systems a much smaller amount of cargo could 

 be carried, and the barrels and boxes were very costly. The later petroleum 

 steamers are commonly spar-decked, and range from 250 to 300 feet in length, and 

 from 1,500 to 2,500 tons gross register. They have their machinery aft, oil-holds 

 up to the main deck, and a long trunk from 10 to 15 feet wide from the main to 

 the spar deck. The latter acts as a feeder, and allows the oil to expand and 

 contract within it without dangerously affecting the vessel's stability. To have 

 the holds half full, with the oil free to wash about, reduces the ship's righting 

 moment, and special care has to be taken in loading and discharging. Water 

 ballast tanks are commonly fitted, and a peculi.ir saddle-shaped tank, patented by 

 Mr. H. F. Swan, has been found specially useful. The oil-hold is divided into 

 compartments by a. centre line bulkbead and by transverse bulkheads about 20 feet 

 apart, and the ordinary structural details are modified in many respects on account 

 of the greater difiicuhies attending oil-tight work. The surveyors of Bureau 

 Veritas have done very much to help forward this industry, while their rivals of 

 Lloyd's Register have remained comparatively inactive. These vessels are all 

 supplied with powerful pumps, and have large oil and water mains led along the 

 main deck, with branches into the holds and connections to meet pipes from the 

 shore. The oil is pumped into large reservoirs at the port of discharge. A cargo 

 may consist of several qualities of nil, and these are separated from each other by 

 narrow water-spaces. The sailing-ship ' Hamaut' was buUt about two years since 



