THE BUILDING OF THE "MONITOR."



similar exposed positions. The exemption from sickness upon the iron-elads
in some instanees is remarkable. There were on1 boardl the Saiqliis, from
November 25th, 1864, to April 1st, 1865,, a period of over four months, but
four eases of sickness (excluding accidental injuries), and of these two were
diseases with which the patients had suffered for years. On the Mifite, for
a period of one hundred and sixty-five days prior to the 29th of May, 1865,
there was but one ( ease of disease oln board. Other vessels of the class exhibit
equally remarkable results, and the conclusion is reached that no woodeu ves-
sels in any squadron throughout the world can show an equal inmunnity from
disease."
  Apart from the ample size of the quarters on board the vessel, shown by
the illustration, it should be mentioned that the system adopted for ventilat-
ing those quarters furnishes an abundant sup1)ly of fresh air by the following
means. Two centrifugal blowers, driven by separate steam-engines, furnished
-ieti thousand cubic feet of atmospheric air per minute by the process of
sun(tion through standing pipes onl deek. Part of the air thus drawli in sup-
pvorted the comlbustion of thle boiler furnaces, the renaiander entering the
lower part of thle hulll, gradually ex pelling the heated and vitiated air within
thle vessel. It has beeti imagined that the fresh air supplied by the blowers
ought to have beeln conveyed to the quarters at the forward end ot thle vessel,
boy a system of cond(ucting pipes. The laws of static balance, however, ren-
der the adoption of such a method unnecessary, since agreeably to those laws
the fresh (0ol( air, unless it be stopled by closed doors in the bulkheads, will
finld its way to every part of the bottoni of the hull, gradually rising and
expellilln the upper heated strata through the hatches, and lastly through the
grated top of the turret.  Naval constructors who speculate on1 the (cause
of the extraordinary healthfulness of the monitors need not extend their
researehes beyond a thorough investigation of the systemt. of ventilation just
des(cribeld.
  Trri'et I)epartiiW t. The most important object delineated on the cenlttral
sec'tion of thet illustration, nanmely, the rotating turret, will now be consi(lered;
but before describing this essential part of the monitor system, it will be well
to observe that the general belief is quite erroneous that a revolving platform,
ol-en or (overed, is a novel design. So far from that being the case, this
obvious dlev1(e dates back to the first introduction of artillery. About
1820 the writer was taught by an instructor in fortification and gunnery
that under certain conditions a position assailable from all sides should be
                                   defended by plaeing the guns oIn a turn-
                                   table. Long before building the ilfoni-
                                   tor I regarded the employment of a
                                   revolving structure to operate guns on
                                   board ships as a device familiar to all
                                   well-informed naval artillerists. But
                                   although constructors of revolving
 SME ELVATION OF A FLOA.TIG REVOLVING CM circular gun-platforms for naval pur-
    CULAR                          peWEn, popIerdD BYn vae e   i    t
            100QXb IN 18(pound;..ps8 open or covered, have a right to



7;8