APPLICATION OF PHOTOGRAPHY TO THE MICROSCOPE. 127 



mitted by the object-glass is diffused over too large a surface, and a 

 faint and unsatisfactory picture results therefrom. Another advantage 

 is, that pictures at this distance are in size very nearly equal to the 

 object seen in the microscope. In some instances better pictures are 

 produced by taking away the eye-piece of the microscope altogether. 

 The time of producing the picture varies from five to twenty seconds 

 with the strength of the daylight. A camphine lamp, light Cannel coal- 

 gas, or the lime-light, will enable a good manipulator to produce pictures 

 nearly equal to the sunlight. Collodion offers the best medium, as a 

 strong negative can be made to produce any number of printed posi- 

 tives. 



The light is transmitted from the mirror through the object and 

 lenses, and brought to a focus on the ground-glass, or prepared surface 

 of collodion, in the usual manner. Care must be taken not to use the 

 burning focus of the lenses. The gas microscope may be used to make 

 an enlarged copy of an object ; it is only necessary to pin up against 

 the screen a piece of prepared calotype paper to receive the reflected 

 image. Mr. Wenham has given directions for improving " microscopic 

 photography" in the Quwrterly Journal of Microscopical Science for 

 January 1855. In this paper he has shown how to ensure quick and 

 accurate focussing ; or, in other words, the making of the actinic and 

 visual foci of the objective coincident. The simplest and cheapest 

 way of producing coincidence is to screw a biconvex lens into the place 

 of the back-stop of the object-glass, acting as part of its optical com- 

 bination. An ordinary spectacle lens, carefully centred and turned 

 down to the required size, answers the purpose exceedingly well. 



Mr. S. Highley's mode of adapting an object-glass to the ordinary 

 camera, for the purpose of taking microscopic objects on collodion and 

 other surfaces, is shown in fig. 91 ; a sectional view of his arrangement 

 is given, which is very compact, steady, and ever ready for immediate 

 use. The tube, a, screws into the flange of a camera which has a range 

 of twenty-four inches ; the front of this tube is closed, and into it screws 

 the object-glass, b. Over a slides another tube, c ; this is closed by a 

 plate, D, which extends beyond the upper and lower circumference of o, 

 and carries a small tube, e, on which the mirror, p, is adjusted. To 

 the upper part of d the fine adjustment G is attached ; this consists of 

 a spring-wire coil acting on an inner tube, to which the stage-plate, 

 H, is fixed, and is regulated by a graduated head, k, acting on a fine 

 screw, likewise attached to the stage-plate, after the manner of Ober- 

 hauser's microscopes. An index, l, is fixed opposite the graduated 

 head, k. The stage and clamp slides vertically on h ; and by sliding 



