HARDWICKE'S SCIENCE-GOSSIP. 



205 



MARKINGS OE THE PODURA SCALE. 



SUCH a question as this, that we all thought 

 was long since a settled one, makes it seem 

 curious to have it asked at the present time. This, 

 however, is not the case ; for those who have read 

 the recent controversy between Dr. Piggott and 

 Mr. Wenham must again, in order to satisfy them- 

 selves, re-investigate the subject, so as to determine 

 whether we are to accept the old ! ! ! markings or 

 the new " beaded " ones as the true markings on 

 the scale. Without determining which is right 

 or wrong, I beg to submit the following twelve 

 different appearances of the scale of the Podura, 

 obtained under every phase of oblique light, as far 

 as I could manage it. I shall now proceed to 

 explain how these results were obtained, and leave 



l-16th objective, made by Powell & Lealand, 

 London, illuminating the scale with Ross's 4-10th 

 achromatic condenser, having 109° aperture, B stop 

 and the concave mirror. These were the means by 

 which I obtained the various markings, which I 

 have roughly sketched and enclosed with this paper 



■flit 



w 



w 



Fig. 112. 



Fig. 113. 



Fig. 114. 



the rest in the hands of those who care to experi- 

 mentalize on this object, and hence determine the 

 truth for themselves. Previously to making my 

 examination of the Podura scale, I did not feel 

 content with having the object mounted with thin 

 glass, as I know false appearances are often ob- 

 tained by the glare from the cover when careful 



Fig. us, 



adjustment of the screw-collar of the objective is 

 omitted to be made. I therefore obtained a fine 

 specimen of the Podura, from which, by letting the 

 insect hop about on a piece of velvet and knock 

 itself against a thin glass slide which I held over 

 it, I obtained a nice supply of scales, not too 

 thickly placed on the slide. I then proceeded to 

 examine this as a dry object, uncovered, under my 

 large Ross A 1 microscope, using an A eye-piece, 



Fig. 118. 



Fig. 119. 



Fig. 120. 



— considering it may be useful at the present time, 

 as the insects are just now abundant, and ready to 

 supply any one who requires it with fine specimens 

 of scales. I conceive these varied figures are the 

 result of peculiar incidences of light upon the 

 object; but still they are interesting, as they show 

 the various effects producible by the play of light 



Fig. 121. 



Fig. 122. 



Fig. 123. 



on such refractive objects. The following is a sum- 

 mary for reference to each scale as it is numbered. 

 Fig. 112 had the light thrown from the left-hand side 

 of the mirror, at an angle of 45°. Pig. 113 had the 

 mirror somewhat more slanted. Pig. 114, light 

 thrown up direct. Pig. 115, light more oblique. 

 Pig. 116, upright scale under same conditions. The 

 rest of the scales were more or less similarly 

 treated, but were lying in various planes to the 

 direction of the oblique light. It was no matter 

 how I "rotated" the scale or changed the mirror, 

 some one of these markings always appeared. 1 

 finally took away the condenser, and then my old 

 friends the ! !! markings returned from their hiding- 

 place, painfully evident ; nor could I with the 

 mirror illumination, though I tried very many 

 ways, resolve the " bulk " of the scales into the 

 new forms which I had obtained by the use of the 

 condenser. In conclusion, I must add, that my 

 investigations were made by night, with a Bel- 



