Trigonometrical Survey. 
4*9 
art. 11. Of the Apparatus provided for the Measurement of 
the Bass. 
The apparatus, provided for the measurement, consisted of 
the following articles, viz. 
1. A transit instrument. 
2. A boning telescope. 
3. Two steel chains, 100 feet each, with the apparatus for 
the drawing-post and weight-post. 
4. Fifteen coffers of deal, for receiving the chain when 
extended in a right line. 
5. Thirty-six strong oaken pickets of gi and 4^ feet long * 
shod, and hooped with iron. 
6 . Four brass register heads, carrying graduated sliders 
moved by finger-screws, for adjusting the ends of the chain. 
One of these registers has a micrometer-screw attached to it, 
proper for measuring small quantities expanded or contracted 
by the chain. 
7. Thirty-six cast iron heads, to fix on the pickets. 
As many of these articles have been described very circurti- 
sfantially by General Roy in the LXXVth and LXXXth Vo- 
lumes of the Philosophical Transactions, it will only be neces- 
sary here to give a description of the transit instrument, bon- 
ing telescope, and the two new chains. 
1. The Transit Instrument. Tab. XLIII. 
This instrument, made by Mr. Ramsden, may be consi- 
dered as a transit combined with a telescopic level, which 
