144 Transactions.— Miscellaneous. 
present. It is probable that measures taken now with the improved position 
circle and the clepsydra, will at all events approach in accuracy the best 
measures taken with perfect appliances. If mercury could be used instead 
of water with similar apparatus, still better results would be obtained, but 
as the object has been to incur as little expense as possible, it has been 
thought advisable to adapt the arrangements to the use of water. 
It is obvious that this method is available for measuring the diameter 
of planets, sun-spots, etc., and also for selenographical observations. 
Art. XI.—Deflection of Shingle-bearing Currents and Protection of River 
Banks by Druslin’s Floating Log Dams. By H. P. Mackin. 
Plate II. 
(Read before the Wellington Philosophical Society, 17th August, 1878.} 
Tue plain of the Wairau in the Province of Marlborough is a tract of flat 
aluvial country, averaging about ten miles by seventy, and has been 
formed on the channel of an ancient iceberg (mer-de-glace), by the streams 
from the surrounding hills and the Wairau River, which traverses its 
entire length, rising on Mount Mackay, and debouching in Cloudy Bay, a 
portion of Cook Strait. Geologically the plain is of post-pliocene formation, 
surrounded towards the north and west by mountains of metamorphic and 
paleozoie origin, and on the south by low hills of marine tertiary drift. 
The Wairau River has evidently formed the greater portion of the plain, 
and carries with it immense quantities of shingle, of which it is made the 
receptacle, by the rivulets from the hills, The district is & prosperous 
farming one; and from its first settlement, has been liable to considerable. 
damage, not only from the flood-water itself, but also from the shifting of 
the river-bed, and the deposit of shingle on the adjacent lands. The town 
of Blenheim is situated on the middle of the plain, and unfortunately, its 
site is lower by several feet than the surrounding country. Every year its 
danger is becoming more imminent, as the beds of the river and its branch, 
the Opawa, are gradually rising, from these rivers being compelled to deposit 
the drift on their banks and beds by lateral embankments. The late 
Provincial Government, under the direction of eminent engineers, has 
tried in vain many devices to direct the stream from the town. All were 
unavailing, as the rapidity of the current undermined cratings, tanks, and 
wing-walls, while the enormous quantities of shingle deposited defied all 
control. Not a wreck remains of ali the works thus erected, costing some 
£15,000. On plan No. I will be seen, at the point X, the lowest point in 
the river bank, whence the town gets flooded by overflow, and where the 
