12 
POPULAR SCIENCE REVIEW. 
mischief occur here, and how is it to be remedied ? It is pro- 
bable that the end of the small bulb was the last point of the 
instrument heated and sealed after the tube had been filled with 
liquid, and that, consequently, the annealing at this point was 
imperfect. It will be of no use, thinks Professor Wyville 
Thomson, to protect this bulb in the same way as the large 
bulb, by an outer shell ; the only plan, therefore, is to thicken 
the small bulb and improve its temper. It should be noted 
that the instrument had undergone a pressure of four tons to the 
square inch, though it had only been tested to bear three tons to 
the same area.* 
With regard to the Bermudas, one would imagine at first 
sight that the islands exhibited on a small scale “ an epitome 
of the geological phenomena of a disturbed palaeozoic district.” 
General (when Lieutenant) Nelson, R.E., has pointed out that the 
great proportion of the Bermudas is formed simply by the 
blowing up by the wind of a fine calcareous sand, a product of 
the disintegration of coral, shells, and other constituents of the 
neighbouring reefs. This sand is blown into dunes 50 feet high 
(“ iEolian formation,” Nelson) — see fig. at p. 267, “Nature,” 
July 31, 1873 — which move inland, “forming shoreward a glacis 
at the angle of repose of loose sand.” This sand is converted 
into a rocky material by the agency of rain-water, which, con- 
taining a quantity of free carbonic acid, dissolves the lime 
freely. This solution of bicarbonate of calcium, on perco- 
lating, loses again a part of its carbonic acid, and deposits a 
cement of carbonate between the particles of coral sand. There 
is a total absence of running water in the Bermudas, nor is there 
a trace of a pool or even of a ditch ; for the rain percolates, as 
through a sieve, the ground, which is also horizontally porous, 
thus letting in the salt water also, below the sea-level. The 
terrestrial vegetation of the Bermudas may, according to Mr. 
Moseley,f be divided into five principal stations, each having a 
flora peculiar to itself ; viz. 1 . To the coast-line, with the littoral 
flora. 2. Peat-bogs or marshes. 3. Shallow brackish ponds. 
4. The caves. 5. The remaining land surface. Along the 
coast-line there occurs abundantly Borrichia , a composite, in 
two forms, side by side ; one with succulent bright green 
f leaves, the other with glaucous and downy foliage. The bind- 
ing plant of the dunes is a hard prickly grass ( Cenchrus ). In 
* It seems that Messrs. Negretti and Zambra had some years previously — 
in 1857 — made upwards of fifty of the same modification of Six’s thermome- 
ters for the Board of Trade. See their letter in “ Nature,” vol. viii. p. 529 ; 
also a communication, accompanied by a figure, “On a New Deep Sea Ther- 
mometer.” — “ Proc. Roy. Soc.” vol. xxii. p. 238. 
f “ Joum. Linn. Soc. Botany,” vol. xiv. No. 77, pp. 317-321. 
