* 
216 REPORT—1874, 
sure steam, with a high degree of expansion and with condensation, was necessary. 
This led to the practical adaptation for the propulsion of vessels of the compound 
engine, an old invention which originated with Hornblower in the latter part of 
last century, and was afterwards further developed by Wolff. The high degrees 
of expansion could not be advantageously used in cylinders heated only by the 
ordinary supply of steam admitted to them for driving the piston; and more espe- 
cially when that steam was boiled off directly from water without the introduction 
of additional heat to it after its evaporation. The knowledge of this, which was 
derived through important advances made in thermodynamic science, led to the 
introduction into ordinary use in steam-navigation of steam-jacketed cylinders, 
and to the ordinary use also of superheated steam. With increased efforts towards 
economy of space in the hold of the ship, which became the more essential when 
very long voyages were to be undertaken, and with the new requirement of greatly 
increased pressure in the steam, the old marine boilers, with their flues of riveted 
plates, were superseded by tubular boilers more compact in their dimensions and 
better adapted for resisting the high pressure of the steam. In connexion with 
these various changes the old difficulty of the growth of stony incrustations in the 
boilers became aggravated rather than in any way diminished. As the only avail- 
able remedy for this, there ensued the practical development and the very general 
introduction of the previously known, hat scarcely at all used, principle of surface- 
condensation instead of condensation by injection. A supply of distilled water from 
the condenser is thus maintained for feeding the boilers, and incrustations are 
avoided. The consumption of coal is often found now to be reduced to about 2 Ibs. 
per indicated horse~power per hour, from having been 4 or 5 lbs. in good engines 
in times previous to about twenty years ago. 
Before the times of ocean telegraph-cables very little had been done in deep- 
sea sounding ; but when the laying of ocean cables came first to be contemplated, 
and when it came afterwards to be realized, the obtaining of numerous soundings 
became a matter of essential practical importance. In the ordinary practice of 
deep-sea sounding, as carried on both before and since the times of ocean telegraph- 
cables, until a year or two ago, a hempen rope or cord was used as the sounding- 
line, and a very heavy sinker, usually weighing from two to four hundredweight, 
was required to draw down the hempen line with sufficient speed, because the 
frictional resistance of the water to that large and rough line moving at any suit- 
able speed was very great. The sinker could not be brought up again from great 
depths ; and arrangements were provided, by means of a kind of trigger-apparatus, 
so that when the bottom was reached the sinker was detached from the line, and 
was left lying lost on the bottom, the line being drawn up without the sinker, but 
with only a tube of no great weight, adapted for receiving and carrying away a 
specimen of the bottom. For the operation of drawing up the hempen line with 
this tube attached, steam-power has been ordinarily used, and practically must be 
regarded as necessary. 
A great improvement has, within the last two or three years, been devised and 
practically developed by Sir William Thomson. Instead of using a hempen sound- 
ing-line, or a cord of any kind, he uses a single steel wire of the kind manufactured 
as pianoforte wire. He has devised a new machine for letting down into the sea 
the wire with its sinker, and for bringing both the wire and the sinker up again 
when the bottom has been reached. With his apparatus, in its earliest arrange- 
ment, and before it had arrived at its present advanced condition of improvement, 
he sounded, in June 1872, in the Bay of Biscay, in a depth of 2700 fathoms, or a 
little more than three miles, and brought up again his sinker of 301bs. weight 
after it had touched the bottom, and brought up also an abundant specimen of 
pe from the bottom, in a suitably arranged tube attached at the lower end of the 
sinker. 
An important feature in his machine consists in a friction-brake arrangement, b 
which an exactly adjusted resistance can be applied to the drum or pulley which 
holds the wire coiled round its circumference, and which, on being allowed to 
revolve, lets the wire run off it down into the sea. The resistance is adjusted so 
as to be always less than enough to bear up the weight of the lead or iron 
sinker, together with the weight of the suspending wire, and more than enough to 
