140 Mr. Troughton on dividing Instruments. 
In doing justice to Bird in this instance, I have only done as 
I would be done by ; for, should any future writer set me 
back a century on the chronological scale of progressive im- 
provement, I hope some one will be found to restore me to 
my proper niche. I now subjoin a re-statement of the greatest 
error of each of the instruments that are brought into compari- 
son by Sir George, after having reduced them all by one rule; 
viz. allowing each of the two points which bound the most 
erroneous extent to divide the apparent error equally between 
them. They are expressed in parts of an inch, and follow 
each other in the order of their accuracy. 
Sir George Shuckburg’s 5 feet standard ,000165 
General Roy’s scale of 42 inches - - ,000240 
Sir George’s Equatorial, 2 feet radius - ,000273 
The Greenwich quadrant, 8 feet radius - ,000465 
Mr. Aubert’s standard, 5 feet long - ,000700 
*The Royal Society’s standard 92 inches long ,000795 
For the justness of the above statement I consider my name 
as pledged ; requesting the permission to say, that if on the 
result of each respective examination, as here presented, there 
could have been more than one opinion, it would not have 
appeared here. I am further prompted to add, that the above 
comparative view presents one circumstance to our notice, 
which cannot do less than gratify every individual who is at 
all conversant in these matters ; I mean, the high rank which 
General Roy’s scale takes in the list ; that scale having been 
made the agent in measuring the base line of our national 
trigonometrical survey. 
* This is the same which Mr. Bird used in dividing his eight feet mural quadrants, 
and was presented to the Royal. Society by Bird’s executors. 
