[ SOS ] 
encounter whatever difficulties and fatigues might attend 
operations carried on in fo inconvenient and inclement a 
fituation. But it Avas requifite I fliould alfo have his Ma- 
jefty’s permiffion for abfenting myfelf fo long from my 
duty at the Royal Obfervatory. This his Majefly was 
gracioufly pleafed to grant; and to allow me to flay as 
long as I thought neceflary, to complete 7fiy very impor* 
iant obfervations. 
Such were the motives for undertaking this experi- 
ment, and the preparations made for putting it in execu- 
tion. I am now to give an account of the operations 
themfelves. 
The quantity of attra6lionof the hill, the grand point to 
be determined, is meafured by the deviation of the plumb- 
line from the perpendicular, occafioned by the attradlion 
of the hill, or by the angle contained between the actual 
perpendicular and that which would have obtained if the 
hill had been away. The meridian zenith diflances of 
fixed ftars, near the zenith, taken Avith a zenith fedlor, 
being of all obfervations hitherto devifed capable of the 
greatefl accuracy, ought by all means to bemadeufe of on 
this occafion : and it is evident, that the zenith inflrument 
fhould be placed direcflly to the North or South of the cen- 
tre of the hill, or nearly fo. In obfervations taken in this 
manner, the zenith diftances of the ftars, or the apparent 
latitude of the Ration, Avill be found as they are affected by 
the attra6lion of the hill. If then we could by any means 
knov/ what the zenith diftances of the fame ftars, or Avhat 
the latitude of the place would have been, if the hill had 
X X X 2 been 
