Popular Science Lectures. 441 
6. — " TIME AND TIME-MEASURERS. 1 
Delivered on Thursday, October igth, by E. A. Pairaudeau, Government 
Surveyor. 
The lecturer commenced by giving concise definitions 
of the two portions of his subject, and shewed the 
necessity for his entering into, and dwelling somewhat 
minutely on, that part of the science of Astronomy which 
treats of the motions of the celestial bodies. During the 
course of this part of the lecture, the details of the 
various periods of Time, such as the Sidereal day, the 
Apparent day, the Mean Solar day or the great standard 
of Time, the week, the month, the year — Sidereal and 
Tropical — were entered into, and an explanation given of 
the use of the transit instrument. One of the various 
methods used — the celebrated pendulum experiment of 
Leon Foucault — to prove the earth's rotation was 
described, and a reference made to the estimate of 
LAPLACE and later Mathematicians, as to the uniformity 
of the earth's diurnal motion during the last 2000 years. 
A comparison was made of this spinning earth as the 
sole occupant of the infinitude of space, with its actual 
position with reference to the subject at issue ; and the 
cause and effect of certain disturbances variously known 
as Precession of the Equinoxes, Nutation and Perturba- 
tion, which affected considerably the apparent motions 
of the celestial bodies, were considered. The meaning 
and the use of the Equation of Time were explained, 
special reference being made to the wonderful, almost 
prophetic, accuracy of the Nautical Almanack, and to 
the manner in which Astronomers in charge of Observa- 
tories obtain the correct time. The difference of time 
