721 



XXIII. — Instantaneous Exposure in Photomicrography. 

 By Walter Bagshaw, F.K.M.S. 



(Read October 18, 1911.) 



Although flash-light has been in common use for purposes of 

 ordinary photography, it has not been tried within the writer's 

 knowledge for photographing through the Microscope, but in the 

 absence of a powerful illuminant, such as the electric light, a ready 

 and simple substitute can be provided whenever the exposure of a 

 fractional part of a second is needed. 



In preparing illustrations of pond life, for example, preference 

 is given to dead specimens mounted without pressure, for the 

 simple reason that a time exposure is impossible with anything 

 not absolutely at rest ; hence, many amateurs will welcome a 

 method that places in their hands a convenient process of photo- 

 graphing objects in motion. 



My first experiment was with fresh-water Polyzoa (Lophopus 

 crystallinus) expanding its tentacles, a movement not too rapid for 

 good definition at ^ second. The Microscope was horizontal, with 

 object in vertical cell on the stage, which was focused by properly 

 adjusted transmitted light from oil lamp in the ordinary way, and 

 provision was made for replacing the lamp by a tin dish containing 

 " Agfa " "Flash Light Powder on a retort-stand arranged to bring 

 the powder in the position previously occupied by centre of lamp- 

 flame, the top of powder being at the level of bottom of flame. 

 Ignition can then be made at a suitable moment by means of a 

 long taper, or red-hot wire. 



To ascertain the most advantageous time for exposure, a dim 

 light should be thrown on the subject obliquely either from behind 

 or in front, sufficient to reveal the outlines when looked at through 

 a hand magnifying glass. The other lights in the room should then 

 be lowered, and the shutter of dark slide withdrawn. Standing in 

 readiness for any desired display of outline, it is easy to fire the 

 powder very quickly. 



Some well-defined negatives were secured when using 2-inch 

 objective and x 5 eyepiece. It is advisable to take precaution 

 against any scattered red-hot particles reaching the Microscope by 

 interposing a sheet of plain glass between the powder and the 

 instrument. The quantity of powder is immaterial, as its com- 

 plete combustion is always g l second, whilst the maximum light 

 develops in less than T i T) second. Only a very little smoke is 

 evolved, which is quickly dispersed. 



In this way I have photographed the larva of caddis fly pro- 

 truding from its case, water shrimps, etc., but I have not yet 

 succeeded in obtaining good definition with darting or rapidly 

 moving objects. I have found no trouble from uneven lighting. 



