402 H. Draper—Diffraction Spectrum Photography. 
wave-length 4850 ten-millionths of a millimeter to 3440. Above 
that is placed a scale, which is a copy of Angstrém’s from just 
below G to H,, with the same-sized divisions carried out from 
H, to O. The 2d, or lower, is a magnified portion of the same 
negative, having H, and H, about its middle, and extending 
from wave-length 4205 to 3736. ae 
It follows therefore that the lines in the solar spectrum are 
correctly represented in their relative positions. The only 
errors are those which may have arisen from mal-adjustment of 
intensities are preserved. 
value of such a map depends on the fact that it not only 
represents parts of the spectrum which are with difficulty per- 
ceived by the eye, (though they may be seen by the methods of 
Stokes and Sekulic,) but also that even in the visible regions 
there is obtained a far more correct delineation in those portions 
which can be photographed. In the finest maps drawn by hand, 
such as those in the celebrated “Spectre Normal du Soleil’ of 
Angstrém, the relative intensity and shading of the lines can 
be but partially represented by the artist, and a most laborious 
and painstaking series of observations and calculations on the 
part of the physicist is necessary to secure approximately cor 
rect positions of the multitude of Fraunhofer lines. Between 
wave-lengths 3925 and 4205, Angstrom shows 118 lines, while 
i 93 
my original negative has at least 293. 
Organization of Plants.” This memoir was accompanied y 
cists have, however, resorted to the plan of taking portion 
the spectrum on a small scale and subsequently making = ‘it 
; : efect 
shading, as well as the omission of fine lines. I 
In the photographs of the spectrum which I have ewe : 
have tried to get as large a portion as I could at once, an" 
as large a scale as possible. I have usually obtained Nees 
