232 



THE AMERICAN MONTHLY 



[December, 



you can read the smallest print in the 

 Great Northern express train. But 

 objects of the millionth of an inch in 

 diameter can be made distinctly visi- 

 ble under special precautions and ar- 

 rangements. Returning then to the 

 general structure of butterfly scales, 

 the pedicel or quill is hollow, and 

 this hollowness, in the shape of 

 canals, radiates more or less from the 

 quill, more or less filled with what 

 I may call butterfly oil or sap, which 

 appears to perform the same office as 

 the sap of plants under the conti'ol of 

 natural forces ; here developing a 

 membrane, there a tube, and many a 

 molecule perhaps helping to keep 

 these tubes expanded. But often 

 through the inadvertent pressure of 

 the nose of the microscope on the 

 delicate glass cover (which for the 

 highest powers is less than half a 

 hundredth of an inch thick) these 

 delicate forms are displaced, spread 

 out, crushed, or distorted ; the con- 

 tents escape, the membraneous en- 

 velope being ruptured, and organic 

 molecules are seen either in heaps or 

 isolated. But marvellous to relate, 

 some of these structures, thus de- 

 formed, have been seen the next day 

 to have resumed their former shape. 

 Within these structures the sap or na- 

 tive oil has been seen flowing up and 

 down in a manner at once demon- 

 strating the oil is contained in a sys- 

 tem of veins or tubules, and within 

 these, occasionally, organic molecules 

 are formed, as shown in the drawings. 

 This movement was caused by the 

 fine adjustment of the microscope in- 

 ducing more or less delicate pressure 

 on the glass-protecting cover. On 

 rare occasions scales may be caught 

 entangled edgeways between the glass 

 slide and this cover, and then the pro- 

 jection of the little villi can sometimes 

 be beautifully seen, at one time side- 

 ways, at another end on, towards the 

 eye of the observer. On one occasion 

 I have seen the ribs on one side in 

 this way corrugated, and on the other 

 side next the insect's body smooth. 

 Besides these general scales, others 



appear inflated like small balloons, 

 and are called battledore scales. The 

 two adjacent, or upper and lower, 

 membranes appear supported and 

 kept from collapsing by a series of 

 little pillars supporting them, attached 

 to opposite ribs ; whilst with my best 

 glasses I have seen the whole surface 

 thickly strewed with minute organic 

 molecules. By the courtesy of Mr. 

 Curties, manager to Mr. Baker, of 

 Holborn, a great number of mounted 

 specimens were obtained for my use. 

 With a power of 3,000 diameters 

 many of the specimens showed mole- 

 cules irregularly distributed upon the 

 membrane near the quill — as bright 

 and translucent as dew-drops. Are 

 many of these rainbow splendors 

 caused by similar optical means.? 

 Myriads of falling raindrops catch the 

 sunbeams, and after internal reflec- 

 tions (one or more) emerge with 

 brilliant prismatic tints — caused by 

 the decomposition of the light by re- 

 fraction after internal reflection. My- 

 riads of transparent molecules here 

 also reflect light with various degrees 

 of brilliance and color. The colors 

 of these creatures are apparently due 

 to a similar cause — reflection and de- 

 composition of solar light. ' Marvel- 

 lous are Thy works ; in wisdom hast 

 Thou made them all.' Very much 

 has been written whether the delicate 

 membrane of these beautiful scales is 

 complex — I mean double quadruple 

 or single. The question seems set- 

 tled by the following facts. The sap 

 flows between the tubes ; scales are 

 apparently a kind of flattened hairs, 

 most of which are more or less hol- 

 low and similarly endowed with mole- 

 cules. Squeezed accidentally, an oily 

 sap escapes. But another fact of an 

 optical nature is still more decisive. 

 Under the very finest instruments ex- 

 tant the former hazy margin of the 

 most delicate scales becomes brilliant- 

 ly clear, sharp, and black — a thin 

 black line about the hundred thou- 

 sandth part of an inch thick. This 

 sharp black line is as precious an in- 

 dication of instrumental pei-fection as 



