456 
Proceedings of the Royal Society 
astronomy, very costly instrumental appliances and a great sacrifice 
of time. And the difficulty of transporting to the Society’s rooms 
from the College the large amount of bulky and delicate apparatus 
required for its proper illustration, is (as I have just found) so 
great, that if on any future occasion the Society desire me to give 
such an address, I shall have to make it a condition that the 
meeting for that evening be held in my class-room in the Uni- 
versity buildings. 
The subject of spectrum analysis must always possess great 
interest for this Society, inasmuch as many of its most distin- 
guished promoters have been, or are, among our Fellows, ordinary 
as well as honorary, and several of the most remarkable memoirs 
on various parts of the subject are to be found among our publica- 
tions. 
The objects of spectrum analysis may be briefly enuntiated as 
follows : — To make, by optical methods , the qualitative chemical ana- 
lysis of (1) a self-luminous body ; (2) an absorbing medium , whether 
self-luminous or not. 
It is difficult now-a-days, when so many philosophers are engaged 
almost simultaneously at the same problem, to decide which of 
their successive steps in advance is that to which should really be 
attached the title of discovery (in its highest sense) as distinguished 
from mere improvement or generalisation. You have only to look 
at the recent voluminous discussions as to the discoverer of the 
Conservation of Energy, to see that critics may substantially agree 
as to facts and dates, while differing in the most extraordinary 
manner as to their deductions from them.* Some of these writers, 
no doubt, put themselves out of court at once by habitually attri- 
buting the gaseous laws of Boyle and Charles to Mariotte and G-ay- 
Lussac. Men who persist in error on a point so absolutely clear 
as this, show themselves unfit to judge in any case of even a little 
more difficulty. Others, who strongly support the so-called claims 
of Mayer in the matter of Conservation of Energy, and who should 
(to be consistent) therefore far more strongly advocate the real 
claims of Talbot, Stokes, Angstrom, Stewart, &c., to the discovery 
of spectrum analysis, are found to uphold Kirchhoff as alone en- 
* Some frantic partisans of Papin, &c., deny almost all credit to Watt in 
the matter of the steam-engine ! No farther examples need be cited. 
