An introduction to the study of the Diatomaceae . adhere. Thus the frustule can be put on the hardeneddrop of gum which has been moistened by the breath ; this isrepeated with a number of valves ad libitum, and finally theyare covered with minute drops of gum till the required thick-ness is attained. This transference of dry frustules upon thedry gum is much easier than the process with fluid gumdescribed under (1), because, with the latter it frequentlyoccurs that in bringing a new frustule into place the othersare disturbed. With uninjured frustules, process (2) is notavailable, because thes
An introduction to the study of the Diatomaceae . adhere. Thus the frustule can be put on the hardeneddrop of gum which has been moistened by the breath ; this isrepeated with a number of valves ad libitum, and finally theyare covered with minute drops of gum till the required thick-ness is attained. This transference of dry frustules upon thedry gum is much easier than the process with fluid gumdescribed under (1), because, with the latter it frequentlyoccurs that in bringing a new frustule into place the othersare disturbed. With uninjured frustules, process (2) is notavailable, because these, after the drying of the thin upperlayer of gum, moistened with the breath, will at once becomecharged with air and baffle any cutting. This absorption ofair can only be avoided by transferring the frustules from thealcohol directly into the fluid gum, which then diffusesequally through them. At the most the frustule at themoment of hardening is slightly compressed, which injuressomewhat the appearance of the section. 6o AN INTRODUCTION TO THE. FIG. 4. STUDY OF THE DIATOMACE^. 61 CHAPTER IX. How to Photograph Diatoms. To photograph Diatoms a camera specially made for thatpurpose will be required. This may either be vertical asshown in Fig. 4 (as used by the author) or horizontal as inFig. 5. The engravings clearly show the construction of thesecameras. Whether one or the other of them be used it shouldbe furnished with two focussing screens, one of ground glass asusual, the other of plain plate glass ; the former being suitedfor roughly getting an idea of the general contour of thespecimen, the latter is used merely as a support for afocussing eye-piece used for focussing the aerial image. Thiseye-piece is adjusted so as to be in focus for a small objectplaced under the opposite side of the plate glass when theeye-piece is held in contact with the other surface of theglass. Just in front of the focussing screen a groove shouldbe cut, permitting of tin plates to be used as mas
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Keywords: ., bo, bookcentury1800, bookdecade1890, bookidintroductiontost00mill
