March 13, 1908] 



SCIENCE 



425 



age about 1/2,500 of an incli in diameter, are 

 spread out in a single layer in almost perfect 

 contact witli each other and are mixed so 

 intimately and in such proportions that light 

 passing through an unobseured plate appears 

 white, or, more strictly speaking, a neutral 

 gray. 



For taking a photograph any ordinary 

 camera may be used but a light orange color 

 screen specially adapted to these plates must 

 be fitted to the lens. The plates must be 

 placed in their holders glass side toward the 

 lens, instead of the reverse as in ordinary 

 plates, so that during the exposure any light 

 which reaches the sensitive film must first en- 

 counter the layer of starch grains, each grain 

 of which will allow the passage of light of 

 its own color and prevent the passage of light 

 of any other color. Owing to the color screen 

 and the still more retarding effect of the starch 

 grains the plates are exceedingly slow and the 

 exposures are from 75 to 100 times or more 

 as long as would be required by the most 

 rapid plates under the same conditions of 

 light. After exposure the plate is developed 

 in total darkness in a pyrogallic acid de- 

 veloper for about two and a half minutes, 

 rinsed in water, and at once placed in a bath 

 of permanganate of potash and sulphuric acid 

 and carried from the darkroom into full day- 

 light. The permanganate of potash and sul- 

 phuric acid mixture rapidly dissolves away 

 the reduced silver in this negative but does 

 not effect the unreduced portion. A second 

 development in daylight, in paramidophenol, 

 or a similar developer working without alkali, 

 results in the reduction of the hitherto un- 

 changed silver salt of the film and produces 

 a positive in which the form and color of the 

 object photographed are accurately reproduced. 

 The colors, however, are generally weak and 

 the plate must be intensified in order to bring 

 them out in full brilliancy. The operations 

 of clearing, fixing, drying and varnishing 

 follow in rapid succession and the transpar- 

 ency is completed. As yet no method of ma- 

 king a colored print on paper has been per- 

 fected, but duplicate transparencies may be 

 made by the ordinary methods. 



As a means of easily and quickly producing 



colored photographs of many kinds of natural 

 history objects this new process presents many 

 advantages and in spite of the cost and short- 

 comings of the plates will doubtless come ex- 

 tensively into use. The exposure required, 

 even under the most favorable conditions and 

 with the most rapid lens, is so long that 

 photographs of moving objects are out of the 

 question. The plates are much less trans- 

 parent than ordinary plates and when used 

 as lantern slides require a stereopticon 

 equipped with a powerful light and placed 

 comparatively close to the screen. Added to 

 these disadvantages is the much more serious 

 one, that the colors of the starch granules, 

 on which the color of the image depends, are 

 not stable and gradually disappear if long 

 subjected to the intense concentrated light of 

 the oxyhydrogen or electric lantern. 



The lantern slides exhibited covered a wide 

 range of siibjeets, such as microphotographs 

 of rock sections, various mineral and organic 

 crystals with polarized light, direct photo- 

 graphs of the solar spectrum, copies of paint- 

 ings, views of beetles, butterflies, shells, 

 flowers, etc., and landscapes, demonstrating 

 conclusively that it is now possible to pho- 

 tograph the color as well as the form of any 

 object and fix them for future reference on a 

 plate which, except under the most trying con- 

 ditions of light, should last indefinitely. 



The next communication, from Dr. P. V. 

 Coville, was on " The Probable Assimilation 

 of Free Nitrogen by the Swamp Blueberry 

 (Vacciniwm corymhosum) ." An abstract on 

 this subject will appear later. 



The last communication, entitled " Some 

 Problems and Possibilities in Hop Culture " 

 was presented by Dr. W. W. Stockberger in 

 the form of a lecture illustrated by lantern 

 slides showing methods of cultivation, harvest- 

 ing and curing the crop, and the comparative 

 growth of local and European varieties on 

 American soils. 



Attention was directed to the desirability of 

 selecting varieties adapted to the various con- 

 ditions of soil and climate, to the influence of 

 seasonal distribution of rainfall on growth 

 and quality and to the necessity of a much 

 broader knowledge of the physiological activi- 



