90 ELEMENTARY PHOTO-MICROGRAPHY. 



advisable to take precaution against any scattered 

 red-hot particles reaching the microscope by inter- 

 posing a sheet of plain glass between the powder 

 and the instrument. The quantity of powder is 

 immaterial, as its complete combustion is always 

 i-3oth second, whilst the maximum light develops 

 in less than i-iooth second. Only a very little 

 smoke is evolved, which is quickly dispersed. In 

 this way I have photographed the larva of caddis 

 fly protruding from its case, water shrimps, etc., 

 but have not yet succeeded in obtaining good 

 definition with darting or rapidly moving objects. 

 There was no trouble from uneven lighting. 



How TO PHOTOGRAPH MULTIPLE IMAGES THROUGH 

 THE COMPOUND EYE OF AN INSECT. 



Gosse, in his book " Evenings at the Micro- 

 scope," states that there are 24,000 lenses in the 

 two eyes of a dragon fly. " Every one of these 

 24,000 bodies represents a perfect eye ; every one 

 is furnished with all the apparatus and combina- 

 tions requisite for perfect vision, and there is no 

 doubt the dragon fly looks through them all." 



This fact is often demonstrated by placing one 

 of these compound eyes, mounted flat on a glass 

 slip, on the stage of the microscope, when any 

 well-defined object may be seen repeated in each 

 of the facets. As a matter of curiosity this is most 



