600 
MR, J. NORMAN LOCKYER ON THE 
X. Wave-lengths and Intensities of the Prominence and Chromo¬ 
sphere Lines. 
Determination of Wave-lengths. 
The wave-lengths throughout are expressed on Rowland’s scale. In the region 
less refrangible than K, they have been determined from the African photographs, 
by comparison with the spectrum of Arcturus and other stars photographed with the 
same instrument, the wave-lengths of the lines in which were determined by reference 
to Rowland’s photographic map. The spectrum of Arcturus is almost identical 
with that of the sun, so that the comparison lines were sufficiently numerous for the 
purpose. Stars like Bellatrix were employed as an additional check in the case of 
bright lines not coincident with prominent Fraunhofer lines. 
Micrometric measurements of the lines were also made and reduced to wave- 
lengths in the usual way, by means of a curve ; these furnished a check on the 
general accuracy. 
In the case of the Brazilian negatives the wave-lengths were determined by means 
of micrometric measures and a curve, and checked by direct comparisons with a 
solar spectrum, photographed with the same spectroscope while it w r as temporarily 
provided with a slit and collimator. 
For the reduction of the ultra-violet, in both series of photographs the wave¬ 
lengths of the hydrogen lines have been assumed as far as from those given 
by Hale,* with the exception of H„, which falls sufficiently near the calculated 
wave-length to be accepted as a hydrogen line. 
With these as datum lines, wave-length curves were constructed, and the wave¬ 
lengths of the other lines found by interpolation. 
The wave-lengths of the radiations more refrangible than were determined from 
extrapolation curves, so that the degree of accuracy is necessarily less than in 
the case of the remaining lines. 
The first column of Table 1. summarizes the wave-lengths of the lines which have 
been measured in all the negatives in both series, whether occurring in the spectrum 
of the chromosphere or prominences. Although the total number of lines photo¬ 
graphed in Brazil is smaller than that photographed in Africa, a few of them only 
appear in the Brazilian photographs; these are at wave-lengths 3674"2, 3679'5, 
3748-5, 4934-2, 5018-6, and 5047-8. 
* ‘ Astronomy and Astrophysics,’ 1892, pp. 50, 602, 61S. 
