534 
increased from twenty-five to sixty-five. 
were ten vessels capable of steaming over 14 knots, now 
there are thirty-five, while the highest speeds have been 
increased from 15 to 17 knots. At the same time the 
power of these vessels of keeping the seas has been 
greatly increased through the improvements which have 
been effected in the economy of the marine engine. 
There are many steamers which can carry coal enough to 
steam round the world at a 10 knot speed. 
The structural strength of merchant vessels has under- 
gone a remarkable improvement during the last few 
years, thanks to the increased attention which has been 
paid to their longitudinal strength, and also to the intro- 
duction of steel as a material of construction and of 
cellular as double bottoms. Doubts have been frequently 
expressed as to the capability of merchant steamers for 
carrying guns. A direct experiment was made on this 
point by the Admiralty in 1878, during the height of the 
Russian scare, by the purchase by the Admiralty of the 
Hecla from Messrs. Harland and Woolf of Belfast. She 
was armed with five 64-pounders and one 4o-pounder, 
mounted on truck carriages, and has been in commission 
ever since, and most favourably reported on. As another 
example we may mention the case of an Irish cattle-boat 
which was purchased by the Chilians and armed with an 
I1-ton gun, and which was employed in the bombardment 
of the Peruvian ports. 
Another most important point in considering the ques- 
tion of the structural strength of these steamers is the 
question of subdivision by water-tight bulkheads. There 
has been a strange apathy on this subject till very recently 
in the mercantile marine. Lloyd’s rules insisted on the 
introduction of four bulkheads, viz. one at each end of the 
ship, and one at each end of the machinery space. The 
compartments into which a ship was thus subdivided 
were in general so large that if one of them filled the 
vessel went down. In many long passenger steamers 
where more numerous bulkheads were introduced, their 
useful effect was done away with by the doors through 
them not being water-tight ; or occasionally by their 
heads being below the water-level. It is however some 
satisfaction to know that all the passenger vessels built 
during the last three or four years for the principal lines 
are properly subdivided. 
It is a matter for regret that Mr. Dunn’s official 
position prevented him from enlightening his audience 
as to the exact degree of useful help which we may look 
for from this auxiliary navy in case of actual need. We 
are also left without any information as the organisation, if 
any, which exists for rapidly equipping and manning 
these vessels whenever their services may be called for. 
Considering the scare which was produced in this country 
in 1878, by the attempt made by the Russians to convert 
a few American merchant steamers of very moderate 
speed into cruisers of the Alabama type, it seems only 
reasonable to hope that, by utilising the immense resources 
of our merchant marine, we may find the means of avoiding 
such panics in the future. 
There were some interesting papers read on the 
subject of marine engines and boilers. Mr. Kirk, of 
the firm of Messrs. J. R. Napier and Sons, of Glas- 
gow, read an interesting paper on the triple expansive | 
or compound engines which he has recently fitted 
to the s.s. Aberdeen; and Mr. Parker, Chief Engineer 
Surveyor to Léoyd’s Register, followed with a general 
paper on the subject of triple and double compound 
engines. Thoughttul students of the steam-engine have 
for some time recognised the fact that one of the principal 
sources of waste in engines which use steam expansively, 
is the variation in temperature of the cylinder, due to the 
difference between the temperature of the steam at the 
pressures at which it enters and leaves the cylinder. The 
greater the difference in these pressures, 7.¢., the greater 
NATURE 
In 1875 there 
[April 6, 1882 
between the initial and final temperatures of the steam. 
The consequence is, that the incoming steam finds the 
cylinder chilled ; a portion of the steam as it enters is con- 
densed, causing a loss of pressure and of useful work. 
As the steam expands and becomes colder than the sur- 
rounding walls of the cylinder, a portion of the condensed 
steam is re-evaporated towards the end of the stroke, and 
during the exhaust when it can do no useful work. Thus the 
cylinder at the commencement of the stroke acts as a con- 
denser, and during the end of the stroke and the exhaust 
as aboiler. It was to obviate the waste due to the above 
causes that the compound engine was introduced. In this 
latter class the steam, instead of being expanded through- 
out in one cylinder, was allowed to expand partially in a 
high pressure, and subsequently in a low pressure cylinder. 
Thus the difference in temperature for each cylinder was 
halved, and the waste due to condensation proportionately 
diminished. By degrees, however, the pressures made 
use of in marine boilers were increased, and consequently 
the range of temperatures even in compound engines 
became as great as in the old simple expansive engine 
using lower pressures. To get over this difficulty Mr. 
Kirk made use of the triple expansive engine, which is 
really a compound engine again compounded, the steam 
being expanded successively in three cylinders. In this 
way the range of temperature is divided into three parts. 
In the case of the Aderdeen the boiler pressure was 125 lbs. 
per square inch, and the diameters of the cylinders were 
respectively 80 in., 45 in., and 70 in., by 4 ft. 6 in. in 
stroke. During a four hours’ trial with Penrikyber Welsh 
coal, the consumption was found to be only 1°25 Ibs. per 
indicated horse power per hour, from which very satis- 
factory result we should be led to expect a sea consump- 
tion of from I°5 to 1°6 Ibs. 
Mr. Milton, of L/oyd’s Register, read a paper on the 
influence of Lloyd’s Rules on marine boiler con- 
struction. This paper was called forth by Mr. Marshall’s 
statement at the Mechanical Engineers’ meeting at New- 
castle, that ‘“‘the ordinary marine boiler, encumbered as 
it is by the regulations of the Board of Trade and of 
Lloyd’s Committee, do-s not admit of much reduction in 
the weight of material or of water carred when working.” 
Mr. Milton has endeavoured with considerable success to 
prove that the above remark, so far at least as it applies - 
to Lloyd's, is far from expressing the truth. He explains 
very clearly the principles on which Lloyd’s base their 
rules. The most important part of his paper is that in 
which he attempts to show that Fairbairn’s rules, as to 
the strength of cylinders pressed from without, are very 
erroneous when applied to flues having the dimensions of 
those of marine boilers. Mr. Milton does not speak hope- 
fully of the use of locomotive boilers for marine purposes. 
Wetrust, for the sake of the country, that his experience 
may not be confirmed by the Admiralty experiments with 
the Polyphemus, which vessel is, as is well known, en- 
tirely fitted with boilers of the locomotive type. 
Mr. W. H. White, Chief Constructor at the Admiralty, 
read a most important paper on the Revision of the 
Tonnage Laws, which we intend to make the subject of 
a separate notice. It was followed by two communica- 
tions from Mr. Martell, Chief Surveyor at Lloyd’s, and 
Mr. W. Rundell, Secretary of the Liverpool Underwriter 
| Register, on the subject of Load Line, a topic which for 
many years past has been the subject of much heated 
argument. Mr. Martell discusses freely the latest pro- 
posals of the Board of Trade, and considers in detail the 
practical considerations which should determine the load 
line for vessels of various clasess. He is of opinion that 
the day has passed for the acceptance by shipowners and 
builders of any scheme for loading which does not take 
cognisance of the for and other elements of a vessel, in 
addition to the length, depth, or size. He winds up his 
| paper with the following sentence, which may well be 
the range of expansion, the greater also is the difference | 
commended to the shipowning community. ‘‘I cannot 
