72 JOURNAL OF PROCEEDINGS. 
This time of rotation is called a sidereal day, and 1s 
measured or determined by two successive transits or passages 
of a star across the meridian of the place, and is sub-divided 
into hours, minutes, etc., called sidereal time. The sidereai 
day may be considered as one revolution of the celestial sphere, 
and every point of it is twice on the meridian at points which 
are 180 degrees distant apart, and it is therefore necessary to 
distinguish between the two transits. The meridian is bisected 
at the poles of the equator, and the transit over that half of the 
meridian, which contains the observer’s zenith, is called the up- 
per transit or culmination. The transit over the other half is 
called the lower transit or culminator. 
The sidereal day begins when the vernal equinox is on, the 
meridian, and may be more accurately defined as the interval 
between two successive returns of that point to the same meri- 
dian. The interval between two successive returns of the sun 
tc the same meridian is called a Solar day. Owing to the mo- 
tion of the Earth in its orbit around the Sun it gives an appar- 
ent motion to the latter eastward among the stars in the celes- 
tial sphere. Hence the Solar day is longer than the Sidereal 
day by the time necessary to catch up to this daily apparent mo- 
tion of the Sun. It is also not uniform, owing to the eccen- 
t: city of the orbit of the earth, and to the Sun moving in the 
ecliptic instead of the equator, equal changes of longitude not 
producing equal changes of R. A. | Now to obtain a uniform 
measure of Solar time a fictitious sun is supposed to move uni- 
formly at such a rate as to return to perigee at the same time as 
the true sun. Another fictitious sun, called mean sun, is sup- 
posed to move uniformly in the equator at the same rate as the 
first fictitious sun, and to return to the Vernal Equinox at the 
same time with it. Then the time denoted by the second, or 
mean sun, is perfectly uniform in its increases and is called 
mean solar time. The time used in Ontario and Quebec is this 
time referred to, the 75th meridian, and is commonly known as 
standard time, and is the time kept by watches and clocks in 
general use. The time denoted by the true sun is called true 
or apparent time. This is the time shown by a sun dial. The 
