2 Transactions of the 



reality of what I observed, which causes me to bring the matter 

 before the notice of my brother microscopists. 



Let me state then, that I see the markings on the ribs of the 

 battledore scales of the "meadow-blue" butterfly as elevations, 

 very much resembhng in shape the vegetable glands seen on the 

 petal of the AnagaUis — a well-known microscopic object; that is, 

 the elevations have a base, a column, and a rounded head, or 

 capital, as I have represented in the drawings on Plate II., and 

 which drawings were carefully made at the time of observation 

 from objects which can be referred to again by means of " Malt- 

 wood's finder." On Plate I. I have given an imaginary con- 

 struction of the battledore scales, with sections, and which are 

 intended to show, what I beheve to be the arrangement of these 

 columnar elevations on the ribs of the scales. Placed as these 

 columns are, perpendicular to the plane of the scale, when they 

 are looked at with the scales lying flat on the glass slide, head, 

 column, and base being in the same axial direction, and in dif- 

 ferent planes, the appearance is much as it is usually represented, 

 a dot upon a flatter dot, and of course more or less indistinct. 

 But if a large number of scales be looked over carefully, some of 

 them will be sure to be found slightly tilted over to one side, and 

 others from accidental causes shghtly bent or distorted, and it is 

 on these scales that the elegant httle columns show most dis- 

 tinctly, being seen more or less in profile. Supposing that a pro- 

 mising scale has been found, it requires, in order to see these 

 markings well, that the illumination should be carefully managed, 

 so as to avoid all obliquity, and the consequent production of 

 heavy shadows, for the purer and 7nore direct the light, the better 

 I have always found true structure to be shown. To get this 

 purity — if I may be allowed to call it so — I always work with a 

 rectangular prism, in the place of the usual plane mirror, and I 

 am careful to place this prism, with its axis strictly at right 

 angles to the direction of the illuminating ray, and I do this more 

 readily by always placing my microscope facing the light, and 

 having a small curtain just in firont of the eye-piece. I should not 

 do this except I found an advantage in it ; and in this position the 

 markings on the battledore scales seemed to me to be more clearly 

 made out when the scale was in a vertical, or nearly vertical, posi- 

 tion on the stage of the microscope. For very perfect vision, 

 light should be most carefully centred, and the proper sized 

 diaphragm stops employed, to cut off all " milkiness " and " glare " 

 from the object, and then compensation should be very exactly 

 made for the refraction of the covering glass, even though this 

 nice operation should be facilitated by the use of the " immersion " 

 principle. When a good scale has been selected, and these deli- 

 cate adjustments attended to, I think the appearances I have de- 



