642 ADDRESS OF PROFESSOR LOVERING. 
the throne of the heaven of matter from the earth to the centre of 
our own little system. If the sun move, a new.order of paral- 
lactic motion springs up in sidereal astronomy. The process of 
elimination requires the mathematician to calculate the direction 
and velocity of the motion of the sun which will leave behind it 
the smallest unexplained residuum: and this remainder is the 
motion of the stars themselves. The delicacy of the problem 
lies in the minuteness of the quantities to be observed and in the 
assumptions which must be made in regard to the distances of the 
stars; only a few of which have been positively computed from 
parallax. However, a result has been reached, highly probable 
in the sun’s case, but which can be converted into absolute values 
for other stars only so fast as their individual distances are dis- 
covered. Here again physics and chemistry, with the spectro- 
scope in hand, have come to the aid of astronomy and geometry. 
Should it appear that the conclusions from spectrum analysis 
must be questioned, the attempt was brave, and even a defeat 
would be honorable. 
In 1675, a Danish astronomer observed the novel fact that 
the frequency in the eclipses of Jupiter’s satellites fluctuated with 
the motion of the planet to or from the earth. He hit upon * 
happy explanation, viz: that the swift light takes more Or less 
time to telegraph the astronomical news across the omnipresent 
lines of force. This early observation is the avant-courier of & 
host.of others which have slowly followed in close array. That 
of a blind musician comes next. He noticed, in 1835, that the 
pitch of .a steam-whistle, on the Lowell Railroad, fell suddenly a8 
the locomotive passed him. Unfortunately, Munroe’s observation 
was never published, although he sought and found an explanation 
of what was then a strange fact. In this case, the whistle sends 
the message, the waves of sound transmit it, and the ear is the 
register: but the changing distance modifies the time. In 1842, 
Doppler of Prague was led, by theoretical considerations, tO for 
mulate the proposition, now known in science as Doppler’s pula 
ciple: that the color of light and the pitch of sound, as they tell 
upon the senses, are changed by the relative velocity of the ob- 
server and the origin of the disturbance. In 1845, Buy Ballo’ 
made experiments upon the railroads in the Netherlands, and 
Scott Russell repeated them on English railroads, which coi 
firmed the theory in the case of sound. In the application of the 
