. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 134 BACTERIA IN RELATION TO PLANT magnification; No. 5, the largest field ; No. 3 will give a sharp image of a flat object a centimeter in diameter. Special condensing lenses are required. These fit into the substage in place of the Abbe condenser. One condenser serves for Nos. 1,2, and 3, and another for Nos. 4 and 5 (fig. 122). In photographing poured-plate colo- nies natural size, there are several ways. It may be done by reflected light, as shown in fig. 123, in which case the colonies sometimes cast deep sh
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 134 BACTERIA IN RELATION TO PLANT magnification; No. 5, the largest field ; No. 3 will give a sharp image of a flat object a centimeter in diameter. Special condensing lenses are required. These fit into the substage in place of the Abbe condenser. One condenser serves for Nos. 1,2, and 3, and another for Nos. 4 and 5 (fig. 122). In photographing poured-plate colo- nies natural size, there are several ways. It may be done by reflected light, as shown in fig. 123, in which case the colonies sometimes cast deep shadows. Such shadows may be avoided by mounting the camera as shown in fig. 124 and gently twirling it during the exposure. The Petri dish may also be photographed by transmitted light ex- actly as if it were a negative for a lantern slide. The Petri dish is then held in place in the darkened window or in front of the camera box by crowd- ing it into a hole cut in a square of thick leather, paper, or sheet-rubber (\ inch), which is then fastened over the kit or framework by eight thumb- tacks, or, better, it may be held in place by two stout rubber bands, as shown in the photographs (plate 17 and fig. 125). With stop 32 u. s. and Seed's 27-X plates the right exposure in Washing- ton is usually somewhere between â J second and 1 second in sunny weather and 3 to 5 seconds in cloudy weather, using a Voigtlaender coUinear lens, series III, No. 6, and south light. Atkinson gets very good results by Fig. 124.' *FjG. 124.âModified Collins-Brown camera swung from the ceiling and set to magnify aliout X iM- The four suspending strings, which are of very strong fish-line, end in an S-shaped hook, the upper end of which hooks (jver a ring attached to a stout cord pendant from the ceiling. The length of bellows in this camera as modified by the writer is 25 inches. The lens used with it is a Zeiss Double-Protar, Series Vila, No. 13, made by Bausch & Lomb, Rochester, N. Y. This is the
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Keywords: ., bookcentury1900, bookdecade1900, bookpublisherwashingtondccarneg
