This method, therefore, I recommend to the study and prosecution of the sailor and philosopher; and the appendant specimen I exhibit to the candid examination of the maritime nations, as a specimen of a general table, showing the variation at all times and places for the whole revolution of the magnetick poles, which I have long ago begun, and, with just encouragement, should have long ago completed.
[1] An account of an attempt to ascertain the longitude at sea, by an exact theory of the variation of the magnetical needle; with a table of variations at the most remarkable cities in Europe, from the year 1660 to 1860. By Zachariah Williams.
CONSIDERATIONS ON THE PLANS OFFERED FOR THE CONSTRUCTION OF BLACKFRIARS BRIDGE.
In three letters, to the printer of the Gazetteer.
LETTER I.
SIR, Dec. 1, 1759.
The plans which have been offered by different architects, of different reputation and abilities, for the construction of the bridge intended to be built at Blackfriars, are, by the rejection of the greater part, now reduced to a small number; in which small number, three are supposed to be much superiour to the rest; so that only three architects are now properly competitors for the honour of this great employment; by two of whom are proposed semicircular, and by the other elliptical arches.
The question is, therefore, whether an elliptical or semicircular arch is to be preferred?
The first excellence of a bridge, built for commerce, over a large river, is strength; for a bridge which cannot stand, however beautiful, will boast its beauty but a little while: the stronger arch is, therefore, to be preferred, and much more to be preferred, if, with greater strength, it has greater beauty.
Those who are acquainted with the mathematical principles of architecture, are not many; and yet fewer are they who will, upon any single occasion, endure any laborious stretch of thought, or harass their minds with unaccustomed investigations. We shall, therefore, attempt to show the weakness of the elliptical arch, by arguments which appeal simply to common reason, and which will yet stand the test of geometrical examination.