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POPULAR SCIENCE MONTHLY. 



absent. In forest air traces of hydrogen 

 were present, and about half as much 

 methane as in the air of Paris. At a 

 mountain station in the Pyrenees at an 

 elevation of 2,785 meters only two vol- 

 umes of methane per 100,000 were 

 found, but seventeen volumes of hydro- 

 gen. At a sea station, 40 kilometers 

 from the coast of Brittany, only traces 

 of methane were found, but nearly two 

 volumes of hydrogen in 10,000, an 

 amount two-thirds as great as that of 

 carbon dioxid. The source and fate of 

 atmospheric hydrogen is a problem 

 which now awaits solution. Liveing 

 and Dewar seem of the opinion that 

 there is a continual accession of hydro- 

 gen to the atmosphere from interplanet- 

 ary space, and Stoney holds that the 

 earth's gravitational attraction is in- 

 sufficient to retain hydrogen in the at- 

 mosphere. Experiments of Gautier 

 show that when certain crystalline 

 rocks are heated with water a consider- 

 able quantity of hydrogen is evolved, 

 which might cause a constant accession 

 of the gas to the atmosphere. The 

 problem must be considered for the 

 present unsolved. 



Professor Nipher, of Washington 

 University, St. Louis, has discovered 

 that the most sensitive photographic 

 plates may be manipulated in open day- 

 light, and perfect pictures may be de- 

 veloped upon them in sunlight instead 

 of in the dark room. The pictures are 

 separately wrapped in black paper in 

 the dark room, and boxed. They may 

 then be separately unwrapped, in the 

 open fields if necessary, and placed in 

 the plate holders. The camera exposure 

 must be very much greater than in the 

 dark room methods. After the exposure, 

 the plate is taken out into the light 

 and placed in the developing solution. 

 Even if direct sunlight falls upon the 

 plate for a moment during these 

 changes, fine pictures may be developed. 

 There is, however, no advantage in un- 

 necessarily exposing the plate. The de- 

 veloping bath may always be in shadow, 

 but beautiful pictures have been de- 



veloped in direct sunlight. The pictures 

 produced in this way are positives, while 

 those produced in the dark room by or- 

 dinary methods are negatives. The posi- 

 tive is the picture ordinarily obtained 

 by printing off from the negative. The 

 shadows show light on the negative and 

 dark on the positive. The positives 

 produced in this way are greatly su- 

 perior to those produced in the dark 

 room on over-exposed plates, and the 

 exposure time is very much less, but 

 may be very great. Such pictvires of a 

 crowded street show the street wth per- 

 fect clearness, every moving thing being 

 eliminated. In one exposure lasting for 

 several hours, a team which had stood 

 in one position for half an hour showed 

 no trace upon the plate when developed. 



Every one who has had experience 

 in photography has lost valuable 

 plates by over-exposure. But Professor 

 Nipher shows that all exposures may 

 be successfully developed. Exposures 

 ranging fi'om a snapshot to an over- 

 exposure of about 2.000 may be devel- 

 oped in the dark room as negatives. The 

 fogging in over-exposed plates is an ap- 

 proach to a zero condition, where the 

 plate is blank. For such exposures 

 bromide is freely used, and a few drops 

 of saturated hypo are added. In ordi- 

 nary dark room work hypo is carefully 

 avoided. But as the zero condition is 

 approached, it is very useful in keeping 

 the plate clear. As soon as the expo- 

 sure is so great that the plate cannot 

 be controlled in the dark room, it may 

 be developed in the light. Plates a 

 million times over-exposed can be thus 

 developed. The amount of illumination 

 of the plate while being developed de- 

 pends upon the amount of exposure in 

 the camera. Instead of using the cam- 

 era, the plate can be exposed in a print- 

 ing frame, where it takes the place of 

 the sensitive paper. An exposure of 

 two or three minutes, just out of direct 

 sunlight at a south window, may be de- 

 veloped in the same light. The best 

 results are obtained with a hydrochi- 

 none developer. Some photographic 



