A Voyage Towards the North Pole Undertaken by His Majesty's Command 1773 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1774 Excerpt: ...with regret, the many im-' perfections of what is called the Azimuth compass. This instrument, though sufficiently accurate to enable us to observe the variations so as to steer the ship without any material error, with the precaution of always using the same compass by which they are taken, is far from being of such a construction as to give the Variation with that degree of precision, which should attend experiments on. which a theory is to be founded, or by which it is to be tried. The observations taken in this voyage will fully evince this, by their great variations from one another in very short intervals of time; nor is this disagreement of successrve observations peculiar to the higher latitudes, and to be imputed to a near approach to the Pole, as I found it to take place even upon the English coast. As to the observations themselves, they were taken with the greatest care, and the most scrupulous attention (O 'to remove every circumstance which might be supposed to create an accidental error; the Observations being taken. 'sometimes by different people with the same compass, in the same and different places; sometimes with different compasses, changing the places and the observers repeatedly, to try whether there was any error to be imputed to local attraction, or the different mode of observation by different persons. I have since my return tried the compasses by a meridian as well as by taking azimuths, and find them to agree with one another, though the same compass sometimes differs from itself a degree in succesfive observations. That every person may (as far as is possible without having been present at the time) be enabled to judge of the degree of accuracy to be expected' in such Observations, as well as the degree of attention paid to tho...