IXVESTIGATIOXS ON LiGHT AND HeAT, MADE AND PCBLTSTTED WHOLLY OR IN PAUT AVITH ArrKOVUlATlON 
FROM THE RrMFonp FrxD. 
» 
\ 
II 
On a Table of Standard Wave Lengths of the Spectral Lines. 
* 
By henry a. RO^YLAXD 
Presented May 10, 1893, 
I 
Some years since, having made a machine for ruhnor gratings and discov(>ml 
the concave grating, which placed in my hands an excellent i^roccss for 
graphing spectra, I applied myself to photograph the f^olar spectrum. The p 
of the concave o-rn.tino-. mounted in the method which I use, of producing a 
lal 
Johns 
spectrum gave me the means of adding a scale of wave lengths, and so producing 
a photographic map of the solar spectrum on a very large scale and of great 
accuracy. I soon after constructed a very much better ruhng engine, which UV 
at a uniform temperature in the vault of the new physical laborafor^ 
Hopkins University, with which I have made very much better grathig^. ^ 1 llier^c- 
fore Avent over the whole process once more, extei 
making nQ\Y negatives of the whole spectrum very 
This set of ten photographic plates is now familiar to most spectro^copist.. ^ 
In order to place the scale on the negatives, it was nece-ary to know the ^.^o^ 
lenoths of certain standard lines. Of course my first thought was of A 
wonder of his time. On trying to place my -ale 
accordincr to his fi-ures, I found it impossible to make them and nij 
ding the map to include L, and 
much better than tlie old. 
J 
O 
wliose measurements were the 
O "-- *-^ 
d I finally was forced to the conclusion 
Avas needed before I could go further. Here again the concave gi 
of standard 
« i. ^^ nni\ rpiitive measures «^iin iii««- 
my rescLie. All the spectra are in focus .at once, and lelafve 
be made at once by micrometric measures of the "^'^''^I^P'"" / ^ ^^ ^,,^d. 
the spectrum is normal, and so a micrometer ot ^tiy i o 
t • . « Astronomy and A.tro-Pl.y.ics," and in the " Ixjndon 
♦ An abstract of this paper has recently appeared m Astroi ) 
■ « 
H 
Philosophical Magazine. 
»• 
VOL XII, 
14 
Ma Bot,. Garden, 
1897. 
