8 National Geographic Magazine. 
Of equal importance with the transit was the Chronometer. 
The expedition was supplied with four of these made by Negus 
of New York. They were regulated to sidereal time, and 
provided with a break circuit arrangement. This consists of a 
toothed wheel acting on a jewel pallet attached to a light steel 
spring. In this spring is a platinum point, which touches another 
platinum point, except when the spring is acted upon by the 
toothed wheel. These points are connected respectively with 
terminals on the outside of the chronometer, and are insulated 
from each other except at their point of contact. The electric 
circuit is complete through the chronometer except when the 
teeth of the wheel acting on the jewel pallet separate the points. 
The circuit is opened for about one-fortieth of a second and closed 
during the rest of the time. One tooth im the wheel is omitted 
and the circuit remains unbroken at that point which is the 
beginning of each minute. Each chronometer is provided with 
a condenser to take up the extra current, and avoid burning the 
contact points. These chronometers were most excellent instru- 
ments, the rate was generally small and very regular, and did not 
seem to be influenced in any way by the passage of the current. 
They are still in use, and are as efficient as ever. 
The expedition was at first provided -with a substitute for the 
chronograph in the shape of the old fashioned Morse telegraph 
register. In this a steel point or stylet was pressed by the action 
of an electro-magnet against a long fillet of paper, unwound by 
clock-work at a rate more or less regular. This magnet was in 
circuit with the chronometer and with a break circuit key in the 
observer’s hand. As long as the electric circuit was closed the 
stylet made a continuous indented straight line on the paper; but 
as soon as it was broken, either by the chronometer or the 
observer’s key, the stylet flew back and left the paper unmarked 
until the circuit was again closed. The effect of the action of the 
chronometer was to graduate the fillet of paper into a series of 
straight indentations, from one to two inches in length, separated 
by unmarked spaces from ;% to ¢ inch in length. When the key 
was pressed an independent clear space was left on the paper, 
and by the relation in distance between the beginning of this 
space and the beginning of the second spaces immediately preced- 
ing and following, the time of pressing the key was determined. 
The omission of the break at the sixtieth second, made the mark 
of double length, and hence the beginning of the minute was 
= sak 
