28 YEAR-BOOK OF FACTS. 



coating of mineral tar, to act both as an adhesive ami an impervious 

 agent. Along the line corresponding to the bottom of the coffer 

 must be joined a flap, to spread over the bottom as f.ir as may be 

 necessary, according to the nature of the bed of the stream. This 

 bed should be raked clear of sticks and stones. Then the usual pro- 

 cess with coffer-dams may be followed. The facility with which the 

 coffer may be taken up and re-established constitutes its great 

 recommendation. 



FLOATING HARBOURS AND BATTERIES. 



A CHEAP mode of constructing Wooden Floating Breakwaters has 

 been submitted to the consideration of Lord Clanricarde's committee 

 of the House of Lords. From printed particulars it appears that 

 the design is that of Captain Adderley Sleigh. The system proposed 

 consists of the use of floating structures, built according to the 

 method adopted in the construction of ships, hollow, water-tight, 

 drawing about three feet of water, their bottom broad and flat, and 

 the seaward side of them presenting to the sea a decked plane in- 

 clined inwards at an angle of from 12° to 15° from the sea level, and 

 rising upwards from the line of floatation at the same angle to the 

 height of about twelve feet; and the decked plane descending in like 

 manner at the same angle below the water to a depth of about ten 

 feet, the whole being moored from that extremity. It is in principle 

 a wedge, of which the point is moored seaward, and it resembles an 

 artificial beach. The cost, it is said, would only be 60/. per yard, 

 instead of 1000/., as the cost of stonework. As outer defences, such 

 wedge-shaped floats, it is conceived, would be useful, as shot would 

 glance off them as they do off the surface of the ocean itself. Coir 

 cables arc recommended for anchoring the structures. "Wind, it is 

 urged, would be deflected as well as waves by the inclined planes 

 presented to seaward, thus securing quiet harbours to landward by 

 means of such breakwaters. No difficulty as to security in mooring 

 is anticipated. — Builder. 



ikon- KAILS in wooden suit's. 

 M. Kmr.MAN asserts that the use of Iron Naila in building 

 Wooden Ships is one of the chief causes of their decay. The i 

 by decay of wood is a process of slow combustion or oxidation ; and 

 M, ELuhlman considers that the iron nails act as carriers for oi 

 and introduce it into the substance of the timber. By contact with 

 water and air the iron is rapidly converted into a sesquiozide. In this 

 state it yields a portion of its oxygen to ;h.- wood, and is redo 



the state of protoxide, which further action of air and moisture con- 

 verts it to the Besquiozide, and so the process goes on, by a sort of 

 catalysis. 



V! I) QUIT-BOATS. 



Mi:. J. D. HlHSOH has p rtain improvements in the 



construction of (inn-boats. Hie object of this invention is so con- 

 structing gun-boats, as that the floating or buoyant part thereof 



