Randel took pride in the precision of his instruments and the resulting measurements. Here he adjusts a chain. “Friday February 9th. The chain on being examined is found to be 0.66 foot too long. Saturday February 10 take out 12 rings and correct the chain.” By this, Randel means that a surveyor’s chain usually had extra loops of wire between the main links of the chain. These extra rings made the chain easier to unfold and refold.
On the opposite page, Randel notes the locations of several buildings along the future course of Tenth Avenue, including a barn and a building owned by Dr. Bradhurst. In the lower left corner of the page, Randel has drawn a square marked “Mon” (for “monument”). He would have set his surveyor’s compass over this monument, then sighted at a corner of each building, recording the bearing shown on the compass-rose. An assistant would then have set out from the monument with a surveyor’s chain and measured the actual distance to that corner. With that length and compass-bearing (and the pre-measured compass-bearing of Tenth Avenue) he could then use trigonometry to construct the right triangle he has sketched in a dashed line. Continuing the process, he comes to find that Dr. Bradhurst’s house fronts onto Tenth Avenue 252 feet distant from the monument—meaning that if Randel’s “Mon” marks the center of an avenue, then the unfortunate Dr. Bradhurst has a house sitting in the middle of a future Manhattan street. BH