100 PROFESSOR PIAZZ1 SMYTH ON 
M. THAten of Upsala, so far as they go. Then come some of my new lines 
from Appendix II., based in part on M. THALEN, and in part upon the old 
standard places of several well-known chemical flames, and a few Solar lines ; 
all of which are appended, for criticism and correction. 
This too is probably very necessary, where extreme accuracy is concerned, 
even among the oldest and longest known lines; as particularly visible in the 
over large numbers for the place of the grand double line of Chlorine, in the 
best known Tabular statements thereof. For no such change of place, we hold, 
could have occurred in consequence of any varied mode of preparing the 
Chlorine, or treating it after being made; but solely from error in reading off 
a micrometer screw, or printing the numbers from MSS. 
CHANGES WITH TIME AND USE. 
So much for endeavouring merely to secure correct numerical accounts at 
the instant, whether in support of, or opposition to, the makers’ labels on the 
tubes. But now we must take up the second part of our promised answer, 
and testify somewhat as to the lasting power of the tubes, and also as to any 
physical changes occurring in them, after their contents had once been formally 
recorded and the record preserved. 
As to general lasting power of the tubes themselves, against the action of 
all ordinary and fair electric currents transmitted through them, and inclusive 
of an immense amount of sometimes not the gentlest handling in transferring 
them from their packing boxes to the electric holder, and vice versd, mcluding 
too, several journeys by rail,—not more than one tube in twenty has failed, 
broken, or become dead—z.e., in all the specimens I have had longest, but 
whose glass-material was rather too soft, too easily fusible, and pervaded with 
some needless impurities. Very recently M. SALLEeron has adopted a harder 
glass ; chiefly for the sake of greater purity in the interior; and that harder 
and less fusible glass is necessarily more brittle. But although it has given 
him an immense amount of trouble in the first formation of the tubes,—yet of 
six completed ones sent to me three months ago, they have stood all the trials 
well, and are exquisitely clear and transparent. 
Next as to the lasting power of the gaseous contents of the tubes, and their 
continued ability to keep on giving out the same spectrum under similar 
illumination,—the principal features of most of the tubes are undoubtedly 
maintained to a great, if not quite an absolute, degree; and large changes 
have only occurred to two or three. But these have been note-worthy. 
To begin with the Cyanogen tube. It was first noted that one of the bulbs 
was very prone to heat when in use; then that the capillary’s light, at first 
brilliantly white, had become faint and pink ; then that the bulbs were becom- | 
