1884.] 



MICKOSCOPICAL JOUENAL. 



231 



is so sensitive that blowing upon the 

 instrument sometimes changes the 

 colors. It shows the bubble black 

 spot, and another person with me has 

 counted thirty-four changes of color 

 between the millionth and the thirty- 

 thousandth part of an inch in thick- 

 ness of the film. This study is most 

 fascinating. But turning to the mag- 

 nificent coloring of the butterflies' 

 wings — let us see if we can get any 

 inkling of the cause of these rich 

 variations in coloi's. Take the azure 

 blue, the flitting denizen of our breezy 

 downs ; viewed against a strong light 

 it is brown. Seen directly by the 

 eye, without a glass or magnifier, it 

 tlarows out a heavenly blue ; but as 

 we increase the power of our appara- 

 tus this color vanishes. The varied 

 prismatic flashings of mother-of-pearl 

 — finely engraved steel — ai^e owing to 

 fine lines. But in the same wing we 

 have these same lines most equally 

 arranged, and yet different portions 

 show every possible variation of color. 

 It is not then in the lines. Where is 

 it then ? In the arrangement and 

 size of these organic molecules and 

 of the striations. For full thirty years 

 of my life have I been straining opti- 

 cal ' powers ' to get a glimpse of min- 

 ute structure unseen before. Here is 

 one ' power ' or objective I have had 

 more than that time, made 40 years 

 ago by Messrs. Powell and Lealand. 

 This showed me minute bodies in- 

 visible generally in more modern 

 glasses. I must detain you a few 

 moments on the size of these mole- 

 cules. Last year, through the kind- 

 ness of Mr. Adams, of Meads, who 

 plaqed at my disposal a number of 

 unusual objects, I discovered the mole- 

 cules of an elephant's hair and those 

 of the hair of the English bats were 

 almost precisely the same size. But 

 in butterfly scales they vary exceed- 

 ingly from the i -40,000th to the i- 

 120,000th of an inch in breadth. In 

 some of the azure blues the structure 

 is exceedingly minute. Now the wave- 

 lets of light are the smallest for blue 

 and the largest for red. Here is a 



hint from Nature. With a power of 

 500 the cross bars can onlv just be 

 descried by daylight with super-excel- 

 lent optical powers. Twenty -one 

 years ago, with the finest glass these 

 opticians could make for me, I 

 thought it a magnificent feat to re- 

 solve these scales into beaded ribs 

 merely. The makers improved the 

 glass after my complaining of a .yel- 

 low fog, the detection of which greatly 

 astonished them ; it will now just 

 show the beaded bars. The scales 

 are mixed with fine delicate yellow 

 ones; these may be young scales. 

 The rich brown of these scales by 

 transmitted light — I mean viewed 

 transparently — is a striking contrast 

 to the rich cerulean blue seen in or- 

 dinary reflected light. One from the 

 West Indies exhibits very small mole- 

 cules indeed. Catching sight of these 

 organic molecules, I repaired to our 

 own willing and distinguished mem- 

 ber, Mr. Muller ; he gladly undertook 

 the dissection of a number of scales 

 by means of chemical reagents. He 

 succeeded in dissolving the material 

 which appeared to cement the struc- 

 tures together. We were rewarded, 

 under the best powers I could muster, 

 with the sight of prominent villi in 

 the scales of several of these insects. 

 The peacock butterfly showed its ribs 

 were formed of innumerable minute 

 bodies. The Amat/izesia showed also 

 without chemical dissection its whole 

 surface covered over with an infinite 

 crop of bodies resembling a thickly 

 sowed bed of mushrooms. The most 

 reliable power of 2,000 diameters dis- 

 tinctly exhibits the stem, base, and 

 head of the Villum. The extraordi- 

 nary difficulty of discerning these 

 bodies has doubtless long prevented 

 microscopists from discovering them. 

 Unfortunately the use of these very 

 high powers is almost impossible in 

 a mixed companv. No one is allowed 

 to move during delicate astronomical 

 work, and you can no more see and 

 discuss the forms of objects the one 

 hundred thousandth of an inch in a 

 vibrating room full of company than 



