Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . he Illustrierte Mitteilungen.) advantage of requiring only one network to interpret the resultsof the various photographs taken with one setting of the camera,but, on the other hand, it labours under the disadvantage that itis impossible to focus the lens on any given object, as it is moreor less a matter of chance what may happen to be in the field ofview. Still there may be cases in which it is necessary to makean exposure directed towa
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . he Illustrierte Mitteilungen.) advantage of requiring only one network to interpret the resultsof the various photographs taken with one setting of the camera,but, on the other hand, it labours under the disadvantage that itis impossible to focus the lens on any given object, as it is moreor less a matter of chance what may happen to be in the field ofview. Still there may be cases in which it is necessary to makean exposure directed towards some particular object. To someextent this may be done by mounting a second mirror on the endof the camera at such an angle that the field of view is reflectedinto the eye; but it will seldom happen that any very certainaim can be taken in this way. Vautier-Dufour and the astronomer Schaer of Geneva havedesigned a novel type of apparatus, intended for use with a longfocus lens. This camera is constructed in two halves, placed oneabove the other. The lens is in the upper half, and the light, PHOTOGRAPHIC OUTFIT FOR BALLOON WORK. 309. Fig. 192. -Vautier-Dufour apparatus, packed in itscase. passing through the lens, is reflected by a mirror at the back ofthe upper half to another mirror at the front of the lower half;it then passes from the lower mirror to the plate at the back ofthe lower half ofthe apparatus. Thelength of thiscamera is, there-fore, only one-thirdof the focal lengthof the lens. Thuswith a lens of focallength 48 in., thecamera wouldmeasure 16 in,from back to front, and with a compact apparatus of this kind,one has all the advantages of the bigger lens. It is needless to say that the camera must be packed in asolid leather case, wellpadded on the inside. Plate-holders. In order to be ableto carry as much ballastas possible, the weightof everything else car-ried in the car must bereduced to a are therefore tobe preferred to glassplates. The weight
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