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POPULAR SCIENCE REVIEW. 
masters of the situation. In considering the influence of these experiments 
on the future of our navy, it must he borne in mind, that although it will 
probably be found to be impossible to clothe frigates of the Warrior type 
with a greater thickness of iron than has already been furnished and 
found vulnerable ; yet, by reducing the height above water, the Americans 
have been enabled to use 7-inch armour-plates, and for the Ericsson 
Monitors , now building, it is said lOb-ineh plates are being employed. 
The question of the relative advantages and disadvantages of the Whit- 
worth, Armstrong, and other guns, has not been advanced a single step by 
the recent trials, although it is now in a fair way for settlement. The 
remarkable results obtained by Mr. Whitworth are almost entirely due to 
the form and material of his projectile, — a form and material employed 
previously by others on a small scale, but with similar results. 
Some remarkable investigations have been made by Mr. Froude, Pro- 
fessor Rankine, and Mr. Crossland, on the motion of waves and the rolling of 
ships. These are much too abstruse for quotation here, and indeed are, 
for the most part, of interest only to the scientific shipbuilder and mathe- 
matician. We may, however, mention an incidental result of Professor 
Rankine’s, which possesses greater claims to popular notice. The height 
of waves is a subject on which savans and sailors have’long had a dispute ; 
the former affirming that, by actual measurement, they do not exceed 
twenty to thirty feet from trough to crest, at the maximum ; the latter, 
who, from their long familiarity with the sea, should know of what they 
speak, maintaining that they constantly rise in storms to a height of a 
hundred feet, or more. M. Michelet not very long ago asserted, with 
warmth and sarcasm, that the off-hand scepticism of scientific men on this 
subject was in exceedingly bad taste, and that the sailors were, in his 
opinion, in the right. Professor Rankine, however, is able to justify his 
scepticism. He shows that, in a vessel floating on waves and rolling 
periodically in consequence of successive impulses, the apparent direction 
and force of gravity undergoes considerable changes. Hence the sensations 
of a passenger in such a vessel — whose body accompanies the vessel in her 
movements, and describes, like each particle of water, a circular orbit,— 
are really the same as if the force of gravity changed in that manner. 
Such a person judges of the height of the crest, and steepness of the 
wave front, not according to the real elevation and position of the crest, 
but according to its perpendicular distance from a plane which seems to 
be level, but which is really very far from horizontal. The sailor, in fact, 
measures the wave in a diagonal direction, which his sensations lead him 
erroneously to believe vertical. “ This delusion seems to account,” says 
Professor Rankine, “ for the exaggerated descriptions which we hear, of 
waves ‘mountains high,’ and which present so strange a contrast to the 
results of accurate measurement. For example, the waves which Dr. 
Scoresby measured in the Atlantic Ocean, and found to be about thirty 
feet high, would seem, when estimated by the eye, under the circumstances 
just mentioned, to be upwards of ninety feet high, and of terrific steepness. 
The same delusive judgment as to the height of waves and the direction of 
gravity accounts also for the appearance, that many have observed, of 
enormous waves seeming to sink, and as it were melt away, just before 
