Description of the Solar Index. 
Size of the several parts of the Instrument. 
Length of the horizontal axis B, 
Diameter of the square part of this axis, 
Height of this axis above the base A, ‘ 
~~ rs ~ tube E, resi. the diameter of the 
Width of ie apis C and D, 
Thickness of these and of the base 7 ; 
Radius of the quadrant, (to the middle of the Hien’ my) 
Breadth of the limb, ; 
arenes bi the pan G and I at the Nitah 
- at the centre, 
ae of the quadrant, ; 
Focal length of the lens, 
Diameter of the lens, 
Distance of the lens from the ous of the ‘quharaint: 
Width of the bar K, ‘ 
Diameter of its pivot, 
The arm LM of the same pid Wik the ag K, 
where it branches from it; but narrows a lit- 
tle toward the vernier. 
The vernier in my instrument is of silver, and sol- 
dered firmly upon the extremity of the arm 
LM, which is shaped so as to receive it. 
Thickness em bar K and of the arm LM, a trifle 
less tha : 
Length of the spit level upon the arm, 
Diameter of the cylindrical portion of the equatorial 
axis at . : . . 
Diameter of do. at R, 
307 
31 inches. 
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That portion of this axis what receives dis idadiane f is} an 
inch wide at the centre of the quadrant, and ,°, of an inch at Q. 
It is first made ,7, of an inch thick, and receives the quadrant im- 
bedded into one side of it about ,!, of an inch; it is then filed 
off on the opposite side till it is left about 7; of an inch thick. 
These dimensions afford an instrument of very proper and 
convenient size; which will be found of easy construction, and 
little liable to get out of order. It can be snugly packed ina 
box about half the size required for the compass,—the equatorial 
