260 Transactions of the Royal Microscopical Society. 



light ; remove the cardboard M, lift the shutter of the dark slide 

 and expose the plate, watching the process through the telescope, 

 and if the exposure is a long one altering anything that may appear 

 necessary, for many beautiful results may be obtained at this stage 

 of the proceedings by altering the light during the exposure. For 

 instance, to mention one which will be at once self-obvious, an 

 object can be exposed first as an opaque specimen and then as a 

 transparent one on the same part of the plate, thus bringing out 

 the surface markings as well as the transparent outlines. The 

 microscope tube and the eye-pieces may be used with the telescope 

 as they should never be used with the microscope in micro-photo- 

 graphy as they contract the field and blur the image, magnifying 

 power being better obtained by distance, which with this apparatus 

 may be anything from 2 feet to 8 feet or more if the table is made 

 long enough. The microscope should be connected to the camera 

 by a cone J, which may be made of tin, paper, or any suitable 

 material. The camera is best made quite open, as shown in the 

 Plate, a cloth being thrown over it supported by the ends and the 

 diaphragms P, P, which are very useful to cut off light not required 

 to form the picture. They should be so arranged as not to inter- 

 fere with the telescope, and may have holes cut in them for this 

 purpose if necessary. A sufficiently strong eye-piece should be 

 used in the telescope to give a clear view of the minutiae of the 

 specimen, so that a very perfect focus may be obtained. Yoiu- 

 hands are the best heliostat, as the mirror is within your easy 

 reach the whole time. Instantaneous micro-photography should 

 be attempted with no objective of a higher power than half an inch, 

 and the large condenser only should be used. The alum or other 

 cell should also be removed at the time of exposure. A special 

 shutter will also be required between the large condenser and the 

 object to be photographed. This shutter should have no connection 

 with the table, as it would communicate a vibration to the whole of 

 the apparatus at the moment when everything should be perfectly 

 still except the movements of the animalcule you wish to photo- 

 graph. A good shutter for this purpose can be made with two 

 boards having round holes cut in them and made to slide one over 

 the other, an india-rubber band being the motive power. In 

 this way one hole may be made to pass the other with such speed 

 that the exposure is absolutely instantaneous, and the portraiture 

 of rapidly moving subjects rendered perfectly easy with a good light. 

 The writer has done many in this way.* Wiien the higher objec- 

 tives are used, such as the yVth, they are generally better used on 

 the immersion piinciple, and glycerine or oil of cassia may be used 

 instead of water. When substances with a higher refractive index 



* Copies of some of tliesc instantanooiis micro-pbotograpLs may be seen in 

 the Indian Museum, Loudou. 



