A METHOD OF PHOTOGRAPHING LEPIDOPTEROUS OVA. 113 



was out of focus, owing to the lack of penetration in the microscopic 

 objective. To improve this I adapted a vapid rectilinear photographic 

 lens of Sin. focus to fit the body tube of the microscope in the place of 

 the usual objective, and as this rendered the stage useless for holding 

 the object to be photographed, as the distance obtainable between it 

 and the lens was much too short for so long focus a lens, I took 

 advantage of the circular opening in the stage to work through, and 

 fixed up a movable slide carrier in proper alignment working 

 behind the supporting block on which the microscope stood. This 

 was a great advance, but I was not, of course, able to get so large a 

 magnification as with the microscopic objective, as, even with the aid 

 of a special extension which I fixed up between the camera lens front 

 and the microscope body tube, which enabled me to obtain a maximum 

 extension of 5ft. between the focussing screen and the lens, I could 

 only get a magnification of about ten diameters, while the exposure 

 required was nearly doubled. On the other hand, I had the advantage 

 of an iris diaphragm in the lens, so that I could focus with this open 

 to the fullest extent and admitting the maximum ainount of light, and 

 then stop down to f. 16 or f. 22 for the exposure, and in this way get 

 the whole of a large ovum like Mimas tiliae or Eatricha ijiierei folia in 

 focus, including even the background. [See plate I., fig. 2, reproduced 

 in the February number of the Entoin. Rn-nnl from Part III of 

 Practical Hints.] 



A very powerful illuminant is an absolute necessity for this kind 

 of work. I started with a paraffin lamp, but soon found this useless, 

 not only on account of the amount of heat it gave out, but also owing 

 to the lack of contrast obtainable in the illumination, and particularly 

 to the very great difficulty in focussing accurately when the ground 

 glass image was so faintly lighted. Fortunately I was able to avail 

 myself of an electric light installation, and found a -25 Amp.-Nernz 

 lamp admirable in every way, as it gave a 25 to 80 candle-power 

 light, and this, with a single condenser on one side of the object and a 

 mirror reflector on the other to reduce the blackness of the shadows it 

 made, appeared as nearly ideal as I could imagine. I have not tried 

 incandescent gas myself, but I understand from friends who use it 

 that it gives equally good results. Still I should imagine that the 

 heat trouble would obtrude itself, especially if the light were placed 

 near to the object, whereas with the Nernz lamp the light can be 

 approached to within Hin. of the ovum being operated on without any 

 untoward results. The great points to bear in mind are to get a 

 brilliant illumination of the object from one side, and a somewhat less 

 powerful lighting on the other, so as to show up the structure and 

 rotundity of the ovum by contrast. The final critical focussing is best 

 accomplished with the aid of a focussing magnifier held aganist the 

 ground glass focussing screen, and fixing the attention on some 

 brightly illuminated spot on the surface of one of the ova to be 

 photographed. 



After focussing and placing the sensitive plate in position, it is 

 only necessary to cover the lens with a piece of black card while 

 drawing out the flap of the dark slide, as any small amount of indirect 

 side light entering the lens is quite negligeable, and the card is more 

 conveniently manipulated than a lens cap. The exposure necessary 

 will naturally vary with the brilliancy of the illumination and the 



