Basak 
S. P. Langley—Allegheny System of Time Signals. 888 
ete. Weights representing three or four seconds are kept on 
the top of the bob, so that their removal will retard the clock 
if desired to that amount. 
A record is kept in which the comparisons in the tabular 
form above given are entered twice daily, the amount of the 
Th meter and clock-case thermometer are also read 
twice daily for the purpose of laying down curves representing 
the separate effects of temperature and pressure. Another curve, 
whose ordinates represent the algebraic sum of the correspond- 
ing ordinates of the first two, shows the combined results of both, 
or comparison with still another representing the clock rates. 
These are chiefly useful in the occasionally long intervals of 
cloudy weather which occur iu winter. At such times the 
clock rates are obtained by interpolation from the curves, and 
“weighted” according to the degree of dependence to be placed 
on each clock, before making up the final or “ adopted error” of 
the standard. When observations are obtained daily, however, 
Such precaution is needless. é 
Those who are aware of the number of patented devices for 
controling distant clocks by electricity, may perhaps feel sur- 
prise that so little mention has here been made of their use. 
Some of these are of extreme ingenuity and much promise, 
