VOL. LXXXV.] PHILOSOPHICAL TRANSACTIONS. 621 



Then follows a table, containing the particulars of the measurement: the first 

 column showing the day of the month when each hypotenuse was finished; the 

 2d, the number of hypotenuses; the 3d, the number of chains in each hypote. 

 nuse; the 4th, the perpendicular belonging to each hypotenuse, or the datum 

 for reducing it to the plane of the horizon; the 5th, the computed reduction; 

 the 6th, the new points of commencement above or below the head of the last 

 picket when a new direction was taken; the 7th, the total descent of the extre- 

 mity of each hypotenuse; and the 8th, remarks, or general occurrences. The 

 result of the whole is, that on 30 measured hypotenuses, the whole reduction 

 on them was 1 .02867 inches. 



In further remarks it is stated that, it having been the wish, that some scien- 

 tific persons should be present at the completion of the measurement, his Grace 

 the Duke of Richmond was pleased to desire Dr. Maskelyne, astronomer royal, 

 and Dr. Hutton, professor of mathematics in the royal military academy at 

 Woolwich, to attend on this occasion; to whom Mr. Ramsden was necessarily 

 joined, as his standard brass scale, and beam compasses, were requisite to con- 

 clude the business with the wished for accuracy. Accordingly, on Wednesday 

 the 28th of September the remaining 3 chains were measured in their presence; 

 and the horizontal distance from the end of the last chain to the axis of the pipe 

 was found to be 21.055 inches, as determined by Mr. Ramsden; and conse- 

 quently the apparent length of the base was 274 chains, and 21.055 inches. 

 The height of the last picket above the pipe was 35 inches, from which deduct 

 ing the 5 inches of the rotten part, which was cut off, there remains 30 inches, 

 or 2-!r feet, for the height of the last picket, above General Roy's pipe; which 

 makes the whole descent 33.55 feet; or about 24- feet more than was determined 

 by the former measurement. The reduction of the base to the temperature of 



62° is then made as follows. 



Feet. 



Apparent length, viz. 2Ti chains + 1.755 feet 27401.755 



Correction for the excess of the chains length above 100 feet, and half their wear, is 



236 X .t9 jti + 38 X .054-89 ,..-., 



ZZ — - — S. 1 ; and this add 2.0539 



The sum of all the degrees shown by the thermometers was 96795.25 ; therefore 



(- — :— -1^^ 54° X 27+) X ■ is the correction for the mean heat in which the 



^5 '12 



base was measured, above 54°, the temperature to which the chains were reduced; and 



this also add 2.8519 



Hence these corrections, added to tlie apparent length, give 27406.6608 



Again, for the reduction of the base to the temperature of 62° we have — x 3.38938 ; 



and this subtract 2.2596 



By the table, the sum of all the corrections for reducing the several hypotenuses to 

 the plane of the horizon is 1.02867 inches = 0.08572 feet; and this subtract 0.0857 



Hence these corrections, taken from the above length, leave that of the base in tlie ~— 



temperature of 02° 27404.3155 



