204 T. P. SMITH ON SOME NEW APPEARANCES IN PODURA SCALE. 



which there could be no doubt, and the same point of the correction 

 collar that gave the sharpest image of this hair gave also the 

 sharpest image of the spines on the scale. Still another proof. 

 To bring the notes of exclamation marks out well requires a deal of 

 management of the light, and are best seen with the smallest 

 apertures of the condenser ; but no amount of light will obliterate 

 the new ones or prevent them from standing out sharply from the 

 general blaze. I may say that the two smallest apertures of my 

 condenser always give false images, and in general work I never 

 use them. 



I have brought two specimens of the scale for your inspection to- 

 night, and have placed one under a T ^" oil immersion and the other 

 under a new dry ■§-". The scale under the y 1 ^-" is doubled up near 

 the quill, and the pointed ends of two or three of the spines have 

 forced their way through the membrane and project by themselves 

 some considerable distance. On the companion scale under the 

 dry -g" you may develop some very respectable beads by using the 

 smallest aperture of the condenser, but they instantly vanish when 

 the light is restored. I have tried the same experiment on the 

 same scale with the oil immersion, but it has too much aperture 

 even then to lend itself to the falsehood. 



Since writing this paper I have spoken to Mr. Pringle — a no 

 mean authority on micro-photography — and he tells me that some 

 time ago he photographed this scale as presenting the same ap- 

 pearance I have been trying to describe to-night, and got severely 

 sat upon in consequence. What I have been calling pins he calls 

 French nails, but the difference is not great. 



