204 PHILOSOPHICAL TRANSACTIONS. [ANNO 1707. 



tinct images of the sun much distended and regularly coloured, just like those 

 described above; the same appearances were observable in all specula, metal and 

 glass, which had these hairs, and I never saw any metal one without some: their 

 size is exceedingly small, not above l75 Vo- of an inch. Rubbing a minute particle 

 of grease on the surface of the speculum, images were seen on the fibrous surface; 

 and they always lay at right angles to that direction in which the grease was disposed 

 by drawing the hand along it. 



Observ. 2. Besides these polished hairs, many specula have fewer or more smaH 

 specks and threads, rough and black. Perhaps every polished surface is studded 

 with a number of small ones, invisible to the naked eye from the quantity of regu- 

 lar light which it reflects. I took, from a reflecting telescope, a small concave 

 speculum not very well finished; its surface showed several specks to the naked eye, 

 and many with a microscope. Its diameter was -§-* of an inch, its focal distance 

 2 inches, and the sphere to which it was ground 8 inches diameter. I placed it at 

 right angles to the sun's rays, coming through a small hole -^ of an inch diameter, 

 into a very well darkened room; I then moved it vertically, so that the .rays might 

 be reflected to a chart 12 inches from the speculum, and consequently 10 from the 

 focus: and though the focus appeared white and bright, yet on the chart the broad 

 image was very different. It was mottled with a vast number of dark spots: these 

 were of 2 sorts chiefly, circular and oblong. Of the former a considerable number 

 were distinct and large, the rest smaller and more confused, but so numerous that 

 they seemed to fill the whole image. None were quite black, but rather of a bluish 

 grey, and the oblong ones had a line of faint light in the middle, just as is the case 

 in shadows of small bodies. But the chief thing I remarked was the colours. 

 Each oblong and round spot was bordered by a gleam of white, and several coloured 

 fringes separated by small dark spaces. The fringes were exactly like those surround- 

 ing the shadows of bodies, of the same shape with the dark space, having the 

 colours in the order, red on the outside, blue or violet in the. inside; the inner- 

 most fringe was broadest, the others decreasing in order from the firsts I could 

 sometimes see 4 of them, and when made at the edge of the large image, I could 

 indistinctly discern the lineaments of a 5th: when 2 of the spots were very near 

 each other, their rings or fringes ran into each other, crossing. 



Observ. 3. When the chart was removed to a greater distance, as 6* feet, the 

 fringes were very distinct and large in proportion ; also the smaller spots became 

 more plain, and their rings were seen, though confusedly, from mixing with each 

 other. When the speculum was turned round horizontally, so that its inclination 

 to the incident rays might be greater, the distance of the chart remaining the same, 

 by being drawn round in a circle, the spots and fringes evidently were distended in 

 breadth. I have endeavoured to exhibit the sun's image, as mottled with fringes 

 or rings and spots, in fig 9. 



Observ. 4. I placed the speculum behind a screen with a hole in it, through 

 which were let pass the homogeneal rays of the sun, separated by refraction through 



