284 Danger of Collision wn Vessels 
ArT. XXITI—On a Discovery for Determining Danger of 
Collision in Vessels Crossing one another's Track. 
Paper contributed by Capt. C. J. PERRY. 
[Read by Professor Halford, Nov. 11th, 1867.] 
Mr. PRESIDENT, 
Sir,—Seven years have elapsed since the writer of this 
paper had the honour of presenting an illustrated treatise 
“ On Collisions at Sea,” to this Society, and on page 18 of 
that work may be seen the author’s justification for publish- 
ing a discovery of very high importance to every maritime 
state in the world, in so limited a manner, as by proffering a 
newly invented instrument for preventing collisions. But, 
of course, the instrument gave effect to the newly discovered 
principle, and the inventor naturally supposed that that prin- 
ciple would be at once seen, and either approved or con- 
demned immediately the instrument should be exhibited in 
public ; but such has not been the case. And although the 
inventor further announced the discovery in the treatise 
(p. 18), by saying: “The process of science is invariably of 
“9 two-fold character, she first of all discovers a law or 
“governing principle by which the operation may be con- 
“trolled, and then constructs an instrument which shall give 
‘effect to that discovery.” Yet, strange to say, no one has 
perceived it, probably because the thing seemed altogether 
incredible. For since during the whole history of navigation 
no nautical writer has ever ventured to propose a means 
within the reach of seamen of knowing when the danger of | 
collision is involved in the courses of two approaching ships, 
it no doubt seemed too much to believe that a mere consi- 
deration of the collision of the “ Lady Bird” and “Cham- 
pion” off Cape Otway, should lead to a discovery of such 
means by a humble individual in the colony of Victoria. 
Again, a person has only to consider the almost unlimited 
diversity in the angle and speed at which ships cross one 
another's track, and above all, the uncertainty which always 
prevails on these points in the mind of the seaman in order 
to understand the apparent improbability of there being any 
mathematical principle in existence, which, in spite of such 
seemingly insuperable difficulties, should be uniformly and 
reliably applicable to every possible case. No wonder then 
that the discovery of such a principle was so far beyond the 
