We have also now marine engines, governed by governors of such extreme
sensitiveness as to give them the semblance of being endowed with the
spirit of prophecy, as they appear rather to be regulating the engine
for that which is about to take place than for that which is taking
place. This may sound a somewhat extravagant statement, but it is so
nearly the truth, that I have hardly gone outside of it in using the
words I have employed. For a marine governor to be of any use, it must
not wait till the stern of the vessel is out of the water before it
acts to check the engine and reduce the speed. Nothing but the most
sensitive, and, indeed, anticipatory action of the governors can
efficiently control marine propulsion. Instances are on record of
vessels having engines without marine governors being detained by
stress of weather at the mouth of the Thames, while vessels having
such governors, of good design, have gone to Newcastle, have come
back, and have found the other vessels still waiting for more
favorable weather.
With respect to condensation in marine engines, it is almost
invariably effected by surface condensers, and thus it is that the
boilers, instead of being fed with salt water as they used to be,
involving continuous blowing off, and frequently the salting up, of
the boiler, are now fed with distilled water. It should be noticed,
however, that in some instances, owing to the absence of a thin
protecting scale upon the tubes and plates, very considerable
corrosion has taken place when distilled water, derived from
condensers having untinned brass tubes, has been used, and where the
water has carried into the boiler fatty acids, arising from the
decomposition of the grease used in the engine; but means are now
employed by which these effects are counteracted.