96 
POPULAR SCIENCE REVIEW. 
Scrope who, in an earlier number commented on his (Mr. Forbes’) lecture on 
volcanoes. Mr. Scrope for the most part agrees with Mr. Forbes, so the 
difference is not great. But on the subject of the formation of volcanic 
sand, of the effect of water on molten lava, and some other points, Mr. Forbes 
here justifies himself fully. 
MECHANICAL SCIENCE. 
Pneumatic Transmission . — A very interesting theoretical paper, on 
systems of pneumatic transmission for passengers and parcels, was read by 
Mr. Robert Sabine at the last meeting of the British Association. The 
results of Mr. Sabine’s examination of the conditions of working of such a 
system may be stated to be : — That small pneumatic tubes may be worked 
more profitably than large ones. For small letter-carrying tubes, and for 
somewhat larger tubes for the transmission of metropolitan letters to branch 
post-offices, he thinks they will undoubtedly work satisfactorily. Large 
tubes of moderate length — for instance for the transport of light goods 
between different parts of a factory — might be found useful. But he does 
not believe that a pneumatic line working through a long tunnel could, for 
passenger traffic, compete, in point of economy, with locomotive railways. 
In a pneumatic tunnel such as that proposed between England and France, 
he estimates that in moving a goods train of 250 tons, at twenty-five miles 
per hour, the mere friction of the air on the walls of the tunnel would 
amount to 93 per cent, of the whole resistance, and the work usefully 
expended in moving the train would be only 5^ per cent, of the whole 
power employed. To propel such a train engines of 2,000 horse power 
would have to be employed at each end, even supposing the blowing 
machinery to act with greater efficiency than has yet been attained. He 
looks to the completion of the Pneumatic Company’s works in London and 
of the pneumatic passenger railway in New York to settle the question of 
the availability of the system for such purposes. The paper will be found 
in Engineering for September 23. 
The Stability of Ships . — The controversy which has followed the cata- 
strophe to the Captain has led to a re-examination of the stability of some 
of the ships in the Navy. The Monarch has proved to have ample stability 
for safety, even at light draught. But when quite light it will contribute 
to her comfort and steadiness, in Mr. Heed’s opinion, to admit water ballast 
into a few of her lower compartments. Provision for effecting this was 
made in her construction. In the four ships of the Vanguard class, Mr. 
Reed believes it will be advantageous to supply them with a certain amount 
of permanent ballast, and for that purpose a layer of iron concrete on the 
bottom is proposed. The need of this ballast arises from the fact that, 
through improvements in the construction, the hulls of these ships are 
really lighter than was anticipated, and they float some inches higher than 
they would have done if these improvements had not been accomplished. 
Thus the expensive wrought-iron work which on the ordinary system of 
construction would have been distributed through the hull, will be replaced 
