is at most 50000000 of an inch, in diameter. Under these circumstances we can not, it would seem, hope at present for any great increase of our knowledge of atoms by improvements in the microscope. With our present instruments we can perceive lines ruled on glass which are 90000 of an inch apart. But, owing to the properties of light itself, the fringes due to interference begin to produce confusion at distances of 74000, and in the brightest part of the spectrum, at little more than 90000, they would make the obscurity more or less complete. If, indeed, we could use the blue rays by themselves, their waves being much shorter, the limit of possible visibility might be extended to 120000; and, as Helmholtz has suggested, this perhaps accounts for Stinde having actually been able to obtain a photographic image of lines only 100000 of an inch apart. This, however, would appear to be the limit, and it would seem, then, that, owing to the physical characters of light, we can scarcely hope for any great improvement so far as the mere visibility of structure is concerned, though in other respects, no doubt, much may be hoped for. At the same time Dallinger and Royston Pigott have shown that, as far as the mere presence of simple objects is concerned, bodies of even smaller dimensions can be perceived. According to the views of Helmholtz, the smallest particle that could be distinctly defined, when associated with others, is about 80000 of an inch in diameter. Now, it has been estimated that a particle of albumen of this size contains 125,000,000 molecules. In the case of such a simple compound as water, the number would be no less than 8,000,000,000. Even then, if we could construct microscopes far more powerful than any we now possess, they could not enable us to obtain by direct vision any idea of the ultimate molecules of matter. The smallest sphere of organic matter which could be clearly defined with our most powerful microscopes may be, in reality, very complex; may be built up of many millions of molecules, and it follows that there may be an almost infinite number of structural characters in organic tissues which we can at present foresee no mode of examining.
Again, it has been shown that animals hear sounds which are beyond the range of our hearing, and that they can perceive the ultra-violet rays which, are invisible to our eyes.
Now, as every ray of homogeneous light which we can perceive at all appears to us as a distinct color, it becomes probable that these ultra-violet rays must make themselves apparent to the ants as a distinct and separate color (of which we can form no idea), but as different from the rest as red is from yellow, or green from violet. The question also arises whether white light to these insects would differ from our white light in containing this addi-
- "Ants, Bees, and Wasps."