Graduation of Agronomical Inflruments • 47- 
that wifh two fets, as a check, will in a great meafure aid 
themfelves, by reading from two different parts of the fame fet 
of divifions; which is very eafily provided for, by putting an 
additional ftroke upon the index plate, at the diftance of 9, 1 1, 
or any prime number of divifions to 19, 23, or more; and 
reading off from that ftroke alfo; as before recommended for 
great quadrants, where the vernier ispropofed to be rejected * : 
fo that they will thereby be mutually checked by divifions that 
had no correfpondence in their original formation, 
* I would not have it thought, from my propofal of reje&ing the vernier, 
that I have any quarrel with it; I think it a very fimple and ingenious contri- 
vance, where it is properly applicable; that is, where the firokes of the vernier, 
or their eftimated halves, are fufficient for all the precifion required or expe&ed 
from the inftrument, as in Hadley’s quadrants, theodolites, &c. : but where 
Hill more minute divifions are required than can eafily be had by efiimation from 
the vernier ; to do this by a fcrew, as a fupplement to the vernier, appears to me 
in the light of bringing a more accurate tool to fupply the deficiencies of one lef® 
accurate; when the former might, with more propriety, fupply the place of th© 
latter altogether. 
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