292 Dr. Barry's Account of the Discoveries of Keber 



of bodies in general would not be shown, and consequently the 

 problem before us would be far from being solved. 



As I further meditated thereupon, in what way I might succeed 

 in dividing the subjects of observation to a degree of minuteness 

 that should answer the requirements above mentioned, I con- 

 cluded to select Nature herself as a guide, and first to consider 

 more intimately such objects as always present themselves in a 

 minutely divided state without artificial aid. Among the first 

 to be considered are undoubtedly the delicate particles of dust, 

 which, in consequence of the gradual weathering of solid bodies, 

 come to hover in the air, and are deposited upon all bodies and 

 everywhere in our dwellings. Now Nature being, as the micro- 

 scope daily shows us, often greatest in the most minute things, 

 and solid bodies being gradually weathered into dust, the said par- 

 ticles of dust appeared to be just a product of the most minute divi- 

 sion of Nature's own preparing, in delicacy such as could scarcely 

 be exceeded, or even reached by art. I therefore devoted myself 

 to the examination of glass, which, after lying from twelve to 

 fourteen hours uncovered, had become slightly dusty. This I 

 did without adding watery and without a covering of glass, under 

 the aplanatic eye-piece of my large microscope by Schick, with 

 200 and 300 times linear magnifying power. The addition of 

 water I omitted, in order not to produce a swelling of the 

 delicate dust particles, and a change in the volume of their 

 pores. The larger dust particles, whose form and compass were 

 most manifold and irregular, it is true, appeared to me almost 

 entirely untransparent, and only at their borders, here and there, 

 diaphanous. On the contrary, in many of the most minute, 

 which likewise presented varied forms, I perceived, on close 

 examination, exceedingly minute spaces and clefts, having a 

 diameter of about the T2V0'" *^ ^^^ TJjn'" (P^^is line), the colour 

 of which, however, principally with bright illumination, mostly 

 exhibited a reddish or greenish tinge. With long examination, 

 I noticed that the borders also of the dust-particles, as well as 

 their finer indentations and inlets, frequently presented exactly 

 the same reddish and greenish edges, and hence concluded that 

 the colouring of those spaces might be owing to interference and 

 flexion of the light, the modifying influence of which on illu- 

 mination was known to microscopic observers long since. This 

 accordance in the colouring of the borders, with that of the 

 apparent spaces in the substance of the dust-particles (which, 

 especially with strong illumination, was often observable also 

 when the microscope was placed at a very considerable distance 

 from the window), could not in my opinion do otherwise than 

 serve as a confirmation of my belief that I here had before me 

 real spaces and minute orifices, even had I upon other grounds 



