180 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
as the canals on Mars are said to be, the eye can see more than the 
photographic plate can record. 
However, the 200-inch will collect so much light that, for the first 
time, it will be possible to photograph enlarged images through filters 
with snapshots. These exposures will be short enough to catch a 
dancing image at the end of a flicker—when it is momentarily at rest 
as it reverses direction. If many exposures are snapped on a movie 
film, a certain percentage of them may be expected to record what the 
eye can see (at least with telescopes of moderate sizes). 
There is much more to the story, but it is too technical for the 
present discussion. But it can be said with some confidence that the 
200-inch may settle the long-standing controversy concerning the 
canals on Mars. 
The second problem I have selected for discussion involves spectrum 
analysis. You know, of course, that light reaches us as a jumble of 
waves of all different wave lengths, each representing a different color. 
It is possible, with prisms or gratings, to spread the colors out into 
an ordered sequence or spectrum, running from the long waves of thered 
to the short waves of the violet, and beyond in either direction. Such 
spectra of stars and nebulae show phenomena of profound significance 
at certain particular wave lengths. Spectrum analysis involves the 
isolation and study of these particular regions. 
Your radio offers an analogy. With the tuning dial you run along 
the spectrum of radio waves and isolate a particular wave length in 
order to hear a particular station which is broadcasting on that wave 
length. 
If there were no tuning device, and you heard all programs at once 
with a nonselective receiver, the result would be bedlam. The step 
from such a nightmare to the clear reception of messages from indi- 
vidual stations suggests the nature of the step in astronomy from the 
study of integrated light to spectrum analysis. 
Light from stars and nebulae originates in atoms. There are as 
many kinds of atoms as there are chemical elements, and the atoms 
may have various stable states. Each stable state of each kind of 
atom represents a set of broadcasting stations, sending messages 
concerning the nature of the atoms and the physical conditions under 
which they exist. By tuning in and reading these messages, it is pos- 
sible to identify chemical elements, to determine temperatures, pres- 
sures, and other physical attributes, and even to measure motion in 
the line of sight (radial velocity). 
But in order to read the messages clearly it is necessary to achieve 
precise tuning—that is, to spread out the spectrum on the maximum 
possible scale. It is here that the great light-gathering power of the 
200-inch offers new possibilities. 
