20 TEMPERATURE AND TIME 
MACGREGOR. 
ART. V.—ON THE MEASUREMENT OF ‘TEMPERATURE AND 
Time — By Pror. J. G. Maccrecor, D:) Se 
(Read March 8, 1887.) 
(Abstract. ) 
THE object of this paper was to point out the analogy 
between the so-called measurement of time and of temperature. 
The time of the occurrence of any event may be described 
by the aid of any series of recurring events. The daily passage 
across the meridian of the first point of Aries may be chosen, 
for example. In that case the time of the occurrence of an 
event is described as between the nth and (m+1)th transits of 
this point. To make the description more definite we may use 
a rapidly oscillating pendulum and describe the event as occur- 
ring between the mth and the (m+1)th oscillations of the pen- 
dulum after the nth transit of the first point of Aries. By 
thus selecting a series of events occurring with sufficient fre- 
quency it is possible to give our descriptions of instants of time 
as great precision as may be desirable. 
It is consequently possible to record the magnitudes of varia- 
ble quantities (e. g. distances, angles, etc.,) at definite instants, and 
therefore to compare the changes which the positions of bodies 
may have undergone in any required interval of time. 
To facilitate the comparison of the contemporaneous changes 
of position or motions of bodies among one another, the motion 
of some one body is chosen as a standard, and all other motions 
are compared with it. It is obviously desirable that the moving 
body chosen as a standard of reference should so move that as 
many as possible of the laws of the motions of other bodies, 
when expressed in terms of its motion, should be (1) simple and 
(2) permanent, i. e., independent of the date of their determina- 
tion. The selection of such a moving body is rendered possible 
by the records of astronomers, which extend over more than 
2000 years. Their observations shew that if the motions of 
