OF VESSELS, OCCASIONED BY LOCAL ATTRACTION. 
219 
ning at the rate of nine knots ; and the first intimation they had of being near 
land, was the jib-boom striking against a high perpendicular cliff, when the 
bowsprit broke short off, the shock sending all three masts over the side;” 
and thus in a moment perished twenty-five valuable lives, and a fine vessel, 
with her cargo, worth nearly a quarter of a million sterling. 
Here then we have a case of a ship leaving port one day, with every pro- 
spect of a fine passage, which had so far lost her reckoning on the evening of 
the next day, as to be wrecked on a rock not more than seventy miles from 
her point of departure, which was supposed to be some miles to her west. 
I have no desire to prejudge the cause of this unfortunate misreckoning; I 
wish only the true cause should be ascertained. In the letter of the com- 
mander of the Thetis to the admiral on the station, he says, that “ from all 
the precautionary measures taken, nothing but the strongest currents, and the 
thick hazy weather, and hard rain, can be pleaded in extenuation.” 
I most sincerely hope that amongst “ the precautionary measures taken,” 
that of correcting or making proper allowance for the local attraction was in- 
cluded; for I have no hesitation in asserting, if such precaution was not taken, 
that this omission would be quite sufficient to account for the accident. It 
is obvious from the general principles which I have stated in the preceding 
part of this paper, that at Rio, where the dip of the needle is about 22° south, 
(the course steered on the 4th of December having been S.E., and on the 
5th of December necessarily somewhere between the east and north,) the local 
attraction would be constantly drawing the vessel over to the westward, and 
there can be no question that her being more to the westward than her reckon- 
ing, was, from whatever source it might have proceeded, the cause of the dis- 
astrous event. 
Without therefore in any way prejudging the case, I have only to express 
a hope that some inquiry may be made, to ascertain whether any and what 
allowance or correction was made for the local attraction of the vessel. 
It is impossible now, if the local attraction of the Thetis has not been be- 
fore taken, to know its amount ; but we can ascertain, at least approximatively, 
what would have been the deflection of the Gloucester under similar circum- 
stances ; and as the amount of attraction in this vessel is nearly the mean of 
all those I have given in a former page, it may be interesting to see the result. 
2 f 2 
