84 On the Trigonometrical Survey 



In the summing up of tlie measurements much labour 

 was occasioned by the divisions of the scale being in inches 

 and four-hundredths, instead of decimals ; but at the time I 

 had no good dividing apparatus, and considered it necessary 

 rather to depend on the divisions of the four-foot standard, 

 (which I had the means of copying on to the scale used 

 for measuring the intervals), the vernier scale alone being 

 divided by such imperfect means as I could obtain. I 

 pursued a better system in the measurement of this Base 

 and the measurement of the base of verification on Norfolk 

 Plains. 



In 1851 the Base at Ralph's Bay was measured. The 

 same rods were used and the same means of determining 

 their lengths, but I had obtained a good dividing apparatus, 

 and I engraved scales, the divisions of which were decimal 

 parts of a foot. These with the verniers read to four 

 places of decimals, the fourth decimal ambiguous, so that 

 the reading was true to the 5000th part of a foot. 



The steel bar, which with other instruments for the 

 trigonometrical operations had been obtained from Eng- 

 land by the Lieutenant-Governor, through the Astronomer- 

 Eoyal, is one of those which were employed as Standards in 

 the measurement of the Base line in Ireland, and the Base 

 line here will therefore be referred to the same standard of 

 measurement. 



The only other improvement introduced was that of 

 attaching a telescope and sights to the rods for keeping 

 them more accurately to the line, and more attention to the 

 piling under the feet of the tressels, where the ground was 

 inclined to shake from the tread of the men in laying the 

 rods. 



The Field Book of the second measurement was much 

 more simple, and the labour of computation much reduced, 



