586 
EDITORIAL OBSERVATIONS. 
physical conditions, or by the presence of other bodies. The 
positions which the lines occupy in the spectrum indicate 
the existence of a chemical property as unalterable as the 
combining weights themselves, and may therefore be 
estimated with almost astronomical precision ; it extends 
almost to infinity the limits within wTiich the chemical 
characteristics of matter have hitherto been confined. Bv 
an application of the method to geological inquiries, the 
most valuable results may be expected; it opens out, more¬ 
over, the investigation of an entirely untrodden field, 
stretching even beyond the solar system, for in order to 
examine the composition of a luminous gas we require, 
according to this method, only to see it; and it is evident 
that the same mode of analysis must be applicable to the 
atmosphere of the sun and of the brighter fixed stars.” 
To give a proof of the extreme delicacy of this method we 
give the following extract : 
“ In a far corner of the experiment-room, the capacity of which was a 
little more than thirty-five feet, was burnt a mixture of three milligrammes 
(00462 gr.) of chlorate of sodium with milk sugar, whilst the non-luminous 
flame of the lamp was observed through the slit of the telescope. Within a 
few minutes the flame, which gradually became pale and yellow, gave a 
distinct yellow sodium line, coincident in the solar spectrum with Fraun¬ 
hofer’s dark line D, lasting for about ten minutes, and then entirely disap¬ 
pearing. From the weight of the sodium salt burnt, and the capacity of the 
room, it was calculated that in one part by weight of air, there was suspended 
less than 35555555 °f a P ar ^ °f s0 ^ a smoke. As the reaction can be quite easily 
observed in one second, and as in this time the quantity of air which is 
heated to ignition by the flame could be calculated from the rate of issue, 
and from the composition of the gases of the flame, the surprising result 
came out that the eye is able to detect with the greatest ease quantities of 
sodium salt less than 3555000 °f a milligramme in weight. The reaction of 
potassium is not nearly so delicate; the spectrum contains only two charac¬ 
teristic lines, one in the uttermost red> and the other far in the violet ray of 
the solar spectrum—points at which the eye ceases to be sensitive to the 
rays. The presence, however, of of a milligramme of the metal could 
be readily detected. Lithium gives two sharply defined lines—the one a 
very weak yellow line, and the other a bright red line, both towards the 
extreme red end of the solar spectrum; though the reaction is not so sensi¬ 
tive as with sodium, it is by far the most delicate test for the metal, the eye 
being capable of distinguishing with absolute certainty a quantity of car- 
