various British standards of linear measure. 77 
Trigonometrical Survey , I thought it preferable to proceed a 
step higher, and to obtain a distance of 40 inches from the 
iron bar itself, which could afterwards be employed in any 
manner that might be found most eligible. 
In order to obviate the necessity of an allowance for tem- 
perature, I caused a triangular bar of cast iron to be made, 
of the same dimensions as Mr. Ramsden’s, except as to 
length. Gold pins were inserted near the extremities of this 
bar at the distance of 40 inches from each other, on which 
were to be drawn fine lines, comprising one sixth part of the 
length of the 20 feet bar. 
The apparatus used for tracing the lines on the gold pins, 
is essentially different from that commonly employed. The 
cutting point is elevated by means of an inclined plane, and 
is then carried through a distance equal to the length of the 
line to be traced. On drawing back a part of the apparatus, 
the extremity of which acts upon the inclined plane, the point 
descends by its own weight until it wholly rests upon the 
surface of the bar ; the motion being then continued, the 
frame and cutting point are drawn along together, without 
the possibility of lateral deviation ; and the point describes a 
line, the length of which may, by a certain contrivance, be 
regulated at pleasure, and its strength determined by repeat- 
ing the operation. This very neat and important invention 
is due to M. Fortin of Paris, and was communicated to me 
by M. Arago, whose liberal mind knows no reserve on scien- 
tific subjects. I have varied the arrangement of M. Fortin, 
so as to bring the cutting point under a microscope furnished 
With cross wires, having an adjustment, by means of which 
their intersection can be brought to the line traced by the 
