On the dip of the magnetic needle in London, in August, 1828

This paper commences by noticing that the Philosophical Transactions contain the record of observations on the dip of the needle in London, from the early part of the last century to the present time. That these observations all concur in showing a progressive decrease of the dip during the whole period in question, but that they are insufficient in number and frequency, and the earlier ones particularly, in the required accuracy to enable us to determine whether the annual decrease has been uniform or otherwise. The author having taken much pains to obtain a correct determination of the dip in the Regent’s Park, in August 1821 (published in the Philosophical Transactions for 1822), repeated his observations in August 1828, at the expiration of seven years from the former determination; an interval which he considered sufficient to throw light on the rate at which the dip is at present diminishing. In consequence of the increase of buildings in the Regent’s Park, he was induced to change the place of observation to the Horticultural Society’s garden, at Chiswick; the distance apart is about five miles, but the direction is as nearly as possible that of the line of equal dip.