88 



0?i the Trigonometrical Survey 



the length of the Longford Base as computed by other tri- 

 angles with its measured length, (the measured length of 

 the four mile base at Ealph's Bay being the given side of 

 the first triangle in each case), and the results are as 

 follows : — 



Measured Length of Longford Base 

 reduced to the Level of the Sea. 



Feet. 

 25,745-7 



Difference in 

 Feet. 



Length as computed by 1st series 



oftriangles 25,746-0 



Do. do. 4th series 25,746-2 



Do. do. 2nd series 25,744-5 



Do. do. 3rd series 25,743-5 



1st Series computed by Mr. Sprent 25,746-01 



1st Series varied in one triangle 



computed by Mr. Sprent 25,745*35 



+ -3 

 + -5 



— 1-2 



— 2-2 

 + -29 



— -35 



The accompanying diagram exhibits the character of the 

 triangles comprising each series; and it will be observed 

 that the series No. 1, composed of the largest and best 

 triangles, give a result the most nearly in accordance with 

 the measurement. The series No. 4 is that from which the 

 next best result was to be expected from the character of the 

 triangles, and it accords most nearly with the first. 



The results of the other two series are very satisfactory, 

 and give abundant proof that both the measurements and the 

 observations are good. With the exception of those at 

 Mona Tower, all the angles used in these computations are 

 taken from the centre of the stations. The angles there 

 were observed out of the centre and reduced. 



In the triangulation to which I have adverted, and in 

 about tlu'ee hundred other calculated triangles, the nearness 

 with which the sum of the triangles corresponds with the sum 

 of 180°, and the spherical excess, gives the greatest proof of 



