120

the principles of bridges.

tract 3-

of the piers: and by them it appears to me, that the insidesof the said piers are filled with rubble; and the external facesare formed with ashler laid in courses: but the rubble ap-pears to be laid with good mortar.

“ George Dance.”

TRACT in.

EXPERIMENTS and observations to be made about

LONDON BRIDGE.

THIS is another of the papers, relating to the state ofLondon bridge, bought at the sale of the late Mr. JohnRobertson’s books. It appears to be an answer given tocertain queries, addressed to the Royal Society from theCommittee of Common Council of the City of London. Thisanswer is signed by the President, the Vice-Presidents, andseveral other respectable members of the Royal Society; viz.by Martin Folkes, esq. the president, and by Wm. Jones(father of the late Sir Wm. Jones), James Jurin, M. D., Geo.Lewis Scott, esq., Benj. Robins, esq., and John Ellicott, esq.,all names highly respectable for their eminent scientific la-bours.—Their report is in the following words:

“ In order to answer the queries proposed by the Com-mittee, with regard to the alterations of London bridge, weapprehend it will be necessary,

“ 1st. To have an exact level taken, between some fixedpoint on the west side of London bridge, and another pointon the east side of Westminster bridge ; as also, to take thelike level between some fixed point on the cast side of Londonbridge, and another point at some convenient place about 2miles below the bridge.

“2. To take the perpendicular height of each of those 4