-T- 
expedient that works quite well. We make contact prints 
from the color transparencies on to glass plates using the 
same emulsions ordinarily used for black and white diaposi- 
tives. The result is a black and white diapositive with 
reversed tone. These emulsions happen to be blue sensitive 
and since the water areas are predominantly blue in tone 
they retain the depth penetration quality of the original 
color transparencies and are quite satisfactory for compi- 
lation of bottom topography on the Kelsh Plotter. 
We look forward to the time when we will have color 
emulsions on a low shrink aerial film base and means of 
making color diapositives for use in stereoscopic plotting 
instruments, but we have not yet received much encouragement 
from industry and this seems to be well into the future. 
We have put color transparencies on the stage plates 
of our stereoplanigraph, covered them with glass plates, 
and obtained a satisfactory model. Our present lights on 
the stereoplanigraph are not satisfactory for this but we 
have ordered new projection-type lamps for these instruments 
and soon will be able to experiment somewhat further with 
this. We do not yet know to what extent film distortion of 
the color transparencies available at present will handicap 
stereoscopic bridging but the ability to bridge even two or 
three models will be helpful in many instances. 
In closing, I want to mention our use of infrared pho- 
tography. For some years now we have found it to be an 
extremely helpful adjunct for mapping the shoreline. This 
is particularly true when we want an exact mean low-water, 
or mean high-water line or for that matter any shoreline 
contour. For charting purposes, the shoreline is the ap- 
proximate mean high-water line which we customarily map 
using panchromatic photography which has been taken in the 
field to identify the shoreline by examination on the ground. 
However, a more exact delineation of the shoreline contour 
is occasionally necessary, and in such cases, we coordinate 
the photography with tide staffs and take infrared photo- 
graphs at, or very nearly at, the exact stage of the tide. 
The contrast between land and water is strong so that the 
shoreline (high-water line, low-water line or any shoreline 
contour) can be accurately mapped with little or no field 
examination. Figures ! and 5 illustrate the facility of 
infrared for this purpose. Figure 4 is a panchromatic pho- 
tograph. Figure 5 is an infrared of the same area.