218 
MR. BARLOW ON THE ERRORS IN THE COURSE 
this disturbing- power; and little, I conceive, need be said to show how much 
such deviations from the estimated course of a vessel, in channels and narrow 
seas, are calculated to lead to the most disastrous events. To take the last 
case, for example, where the deviation is 9° 30', and for the deviation in miles 
the general expression (dist. X 2 sin ^ deviation), we shall find that after run- 
ning ten miles, the vessel would be more than a mile and a half to the south- 
ward of her reckoning ; in a distance of twenty miles, three miles and a quarter 
to the southward ; in thirty miles, five miles to the southward, and so on as 
the distance increases. 
Now it requires no knowledge of navigation to estimate the fatal conse- 
quences that might attend such an error in a narrow channel and in a dark 
night, if it were wholly unknown or disregarded. We see also how very easy 
it is, after an accident has occurred, to imagine a current (unknown of course 
to exist before), to account for the disaster. The Gloucester, for example, in 
the above instance was constantly “drawn to the southward;” and this might 
have been set down to the effect of a current, had it not been proved to be 
local attraction. 
That a ship is sometimes involved in an unknown or unusual current, which 
may lead her into an error of reckoning, no one can for a moment deny ; but 
I do at the same time maintain, that unless a proper attention be paid to the 
local attraction, a vessel is as it were in a perpetual current, setting some- 
times in one direction, and sometimes in another, sufficient to baffle the most 
experienced pilot ; and I further maintain, that science and humanity both re- 
quire, before we admit the plea of unknown currents to explain the cause of 
every disaster, that it be sufficiently ascertained how far allowance has been 
made, or a correction obtained for that current, which it is now well known 
a vessel carries with her through every league of her voyage. 
Let us now turn to the late melancholy wreck of His Majesty’s ship Thetis. 
It appears from the account given of this disaster in the United Service Jour- 
nal, that “ the Thetis sailed from Rio Janeiro on the 4th of December, with a 
million of dollars on board, besides other treasure, and every prospect of a fine 
passage, stretching away to the S.E. The next day, the wind coming rather 
favourable, they tacked, thinking themselves clear of land ; and so confident 
were they, that the top-mast studding sails were ordered to be set, the ship run- 
